Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “internalization”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1999

International harmonization of standards for diagnostic tests and vaccines: role of the Office International des Epizooties (OIE).

The OIE is recognized as the world organization for animal health. Serving 145 member countries, the OIE provides current information on disease occurrence, coordinates studies on disease surveillance and control, and harmonizes regulations for trade in animals and animal products. This paper focuses on the role of one the OIE's specialist commissions, the Standards Commission. The Standards Commission works in close collaboration with the Scientific and Technical Department of the OIE's Central Bureau on the international harmonization of standards for diagnostic tests and vaccines. The Manual of Standards for Diagnostic Tests and Vaccines, approved by the International Committee, defines the international standards for diagnostic tests and for the production of biological products as applied to mammals, birds, and bees. The Manual lists and details those tests which are prescribed for international trade and others which are suitable for bilateral trade agreements. The Manual represents one of the key scientific and technical references for harmonization of regulations for trade in animals and animal products. The commission coordinates the activities of a network of some 110 OIE reference laboratories and six collaborating centers. By creating and nurturing this network, international harmonization is promoted through the sharing of knowledge and the establishment of collaborative projects related to methods development and standardization, production and distribution of international reference standards, quality assurance, and assay validation. Through a series of guidelines provided to participants, the commission ensures the quality and focus of these projects. In matters of a scientific and technical nature concerning diagnostic tests and vaccines, the Standards Commission collaborates with other international organizations such as the FAO, WHO, IICA, and PAHO, thus promoting harmonization at the international program level. Underscoring the important role of the OIE at this level, the Sanitary and Phytosanitary Agreement of the World Trade Organization, as included in the Marrakech agreement (1994), specifically recommends the use of standards, guidelines, and recommendations developed under the auspices of the OIE in order to promote harmonization of regulations for trade in animals and animal products.

Animal Diseases↗
PubMed1992

General internal medicine and general internists: recognizing a national need. Federated Council for Internal Medicine.

The Federated Council for Internal Medicine (FCIM) comprises the American Board of Internal Medicine, American College of Physicians, American Society of Internal Medicine, Association of Professors of Medicine, Association of Program Directors in Internal Medicine, and the Society of General Internal Medicine. The Council was established in 1975 to speak with a collective voice for the specialty of internal medicine. In 1992, the Council developed the following statement in conjunction with its endorsement of a target of 50% of internal medicine residency graduates entering the practice of general internal medicine.

Career Choice↗
PubMed1994

The National Study of Internal Medicine Manpower: XX. The changing demographics of internal medicine residency training programs.

Three annual physician workforce surveys of internal medicine residency programs from 1990-1991, 1991-1992, and 1992-1993 show that changes in the demographic characteristics of internal medicine residents detected in the period 1986-1989 have been sustained; specifically, more women and international medical graduates are entering internal medicine. Women and international medical graduates now compose 32% and 36% of internal medicine trainees, respectively. The percentage of U.S. medical graduates was lower in traditional 3-year (categorical) tracks (64%) and highest in preliminary tracks (1 year of internal medicine leading to another specialty) (87%). Approximately 1500 more first-year residents than positions offered through the National Residency Matching Program were reported in 1992-1993. This suggests that many programs concentrate their recruiting efforts outside the Matching Program. The data also show a continuing high subspecialization rate for residents who complete 3 years of training in internal medicine (approximately 60%), although about one third do not go directly into subspecialty training. We discuss the implications of these findings for the national goal of increasing the number of primary care physicians.

Career Choice↗
PubMed1989

[A case report of hypoplasia of the root portion and the intermediate portion of the left internal carotid artery associated with an unusual primitive collateral circulation between the left internal carotid artery and the left external carotid artery].

The internal carotid artery is one of the most stable arteries and its absence is very rare. We reported a case of hypoplasia of the root portion and the intermediate portion of the left internal carotid artery associated with an usual primitive collateral circulation between the left internal carotid artery and the left external carotid artery. A 57-year-old male developed right hemiparesis of sudden onset 3 days prior to admission. On admission, right hemiparesis and right minimal facial palsy was observed. The left direct carotid angiogram revealed that the root portion and the intermediate portion of the left internal carotid artery were hypoplastic. There was an unusual primitive collateral circulation between the left internal carotid artery and the left external carotid artery. From an embryological point of view, normally, the internal carotid artery is derived from the third aortic arch and the dorsal aorta when the embryo is attained the 3-mm stage. The root portion of the internal carotid artery is formed from the third aortic arch. The dorsal aorta between the third and the first aortic arch form the intermediate portion. The distal part of the internal carotid artery originates from the dorsal end of the first aortic arch. The common carotid artery begins to form in the 12-mm to 14-mm embryo, following involution of portion of the ventral aortic root between the third and the fourth aortic arch. The external carotid artery arises from the aortic sac and migrate up to the third aortic arch.(ABSTRACT TRUNCATED AT 250 WORDS)

Aorta, Thoracic↗
PubMed1993

Selection of internalization-deficient cells by interleukin-2-Pseudomonas exotoxin chimeric protein: the cytoplasmic domain of the interleukin-2 receptor beta chain does not contribute to internalization of interleukin-2.

To study the structural basis of ligand-induced receptor-mediated internalization of interleukin-2 (IL-2), a strategy has been developed to generate variant T cells that are deficient in internalization of this cytokine. IL-2 receptor (IL-2R) alpha- and beta-bearing EL4 cells, that express high-affinity IL-2R and internalize IL-2, were treated with low doses of IL-2-Pseudomonas exotoxin chimeric protein (IL-2-PE40). This treatment resulted in isolation of a variant (CX1) that was unable to express high-affinity IL-2R or internalize IL-2. Transfection of CX1 with the IL-2R beta cDNA led to surface expression of IL-2R beta and high-affinity IL-2R as well as the ability to internalize IL-2. This finding indicates that the absence of the beta subunit was the sole defect in CX1 responsible for its failure to internalize IL-2. By transfecting CX1 with mutated beta cDNA, several CX1 transfectants were produced that expressed a beta-subunit that lacked all amino acids of the intracytoplasmic region. These transfectants expressed high-affinity IL-2R and internalized IL-2 at a rate comparable to cells expressing wild-type beta-chain. These results demonstrate that internalization of IL-2 is independent of any signals contained in the intracytoplasmic tail of the beta subunit and raise the possibility that such signals may be entirely contained within the gamma subunit.

Amino Acid Sequence↗
PubMed1993

The First International Standard for Antitetanus Immunoglobulin, Human; pharmaceutical evaluation and international collaborative study.

The First International Standard (IS) for Antitetanus Immunoglobulin, Human (coded 26/488) was established by the WHO Expert Committee on Biological Standardization in October 1992 on the basis of an extensive pharmaceutical evaluation and an international collaborative study. Fifteen laboratories from 15 countries performed the toxin neutralization assay in vivo in the study. Twelve laboratories also performed an alternative in vitro assay. The new International Standard is a purified human immunoglobulin containing antibodies which are able to neutralize tetanus toxin. This new standard replaces the Second International Standard for Tetanus antitoxin, Equine, for testing of human antitetanus immunoglobulin preparations used clinically as well as for titration of human serum samples for tetanus antitoxin. The new International Standard was assigned a potency of 120 International Units (IU) of Tetanus Antitoxin per ampoule on the basis of its calibration in terms of the International Unit defined by the Second International Standard for Tetanus Antitoxin, Equine by toxin neutralization assay in vivo. The same preparation was also established as the first European Pharmacopoeia Standard for Antitetanus Immunoglobulin, Human by the European Pharmacopoeia Commission, Biological Standardization Programme in March 1993.

Animals↗
PubMed1992

Receptor-mediated internalization of bradykinin. DDT1 MF-2 smooth muscle cells process internalized bradykinin via multiple degradative pathways.

This study was undertaken to evaluate the role of internalization in the action of the peptide autacoid bradykinin (BK). At 4 degrees C [3H]BK binds to an apparently single class of B2 kinin receptors on DDT1 MF-2 smooth muscle cells (C. M. Munoz, S. Cotecchia, and L. M. F. Leeb-Lundberg, manuscript submitted). At this temperature the [3H]BK binding was confined exclusively to the cell surface. On the other hand, at 37 degrees C the B2 receptor-specific cell surface [3H]BK binding was rapidly followed by a receptor-specific internalization of [3H]BK (t1/2 approximately 9 min). The internalization reached a steady-state level after 30-40 min that was 80-100% of the level of specifically bound [3H]BK on the cell surface at 4 degrees C, and this level was maintained for greater than or equal to 2 h. Internalized [3H]BK was routed via at least two intracellular degradative pathways which were distinguished primarily based on subcellular localization but also on a small but significant difference in the rate of [3H]BK degradation. One pathway was localized in a plasma membrane-enriched fraction and had a relatively high degradative capacity. Another pathway was localized in a microsomal fraction and had a relatively low degradative capacity. The internalized [3H]BK activity was rapidly released into the media (t1/2 approximately 24 min). Following a single round of internalization, the released activity consisted almost exclusively of small [3H]BK fragments (less than [3H]BK(1-5)). In contrast, at steady-state [3H]BK represented 30-40% of the released activity. While chloroquine (100 microM) did not alter the rate of [3H]BK internalization or release or the intracellular distribution of [3H]BK, this agent significantly decreased the rate of [3H]BK degradation in both pathways. In all, these results show that B2 kinin receptor-mediated internalization of BK is a process integral to the interaction of BK with DDT1 MF-2 smooth muscle cells and may be a mechanism for terminating BK actions by rapidly removing extracellular free and receptor-bound BK and accessing various intracellular BK degradative pathways.

Amino Acid Sequence↗
PubMed1993

Concomitant defect in internal release and influx of calcium in patients with congenital platelet dysfunction and impaired agonist-induced calcium mobilization. Thromboxane production is not required for internal release of calcium.

The rise in cytoplasmic ionized calcium concentration ([Ca2+]i) on platelet activation is a combination of Ca2+ release from internal stores and influx of extracellular Ca2+. To understand the underlying mechanisms, we studied internal release and influx of Ca2+ in platelets from four patients with impaired agonist-induced Ca2+ mobilization and abnormal platelet aggregation and secretion responses. In normal platelets, thrombin caused a dose-dependent increase in internal release and influx; aspirin inhibited the total rise in [Ca2+]i and influx but not internal release, indicating that internal release occurs independent of cyclooxygenase products. In the four patients, both internal release and influx of Ca2+ induced by thrombin and adenosine diphosphate were diminished; the defect was more striking at lower agonist concentrations. To determine whether the Ca2+ storage organelles of these platelets had a diminished responsiveness to inositol 1,4,5-triphosphate (IP3) we studied IP3 (0.05 to 5 mumol/L) induced Ca2+ release and found it to be normal in all patients. We conclude that the impaired Ca2+ mobilization in our patients is due to abnormalities in both internal release and influx and that it is unlikely to be due to impaired platelet responsiveness to IP3 or defective thromboxane production. The impaired Ca2+ mobilization may be due to defects in phospholipase C activation and IP3 production. These patients provide direct evidence that internal release and influx of Ca2+ on platelet activation are closely interrelated.

Blood Platelet Disorders↗
PubMed1992

Rabies vaccine standardization: International Collaborative Study for the Characterization of the fifth International Standard for Rabies Vaccine.

A collaborative study was carried out to establish a replacement for the International Standard for Rabies Vaccine, the stocks of which are exhausted. Three rabies vaccines for human use derived from different rabies virus strains and prepared on different cell culture substrates were compared with the International Standard for Rabies Vaccine using in vivo and in vitro assay methods in a collaborative study involving 14 participants. The proposed fifth International Standard (PISRAV) which was derived from the same virus strain as the present international standard preparation, the Pitman Moore (PM) strain, was found to be approximately twice as potent relative to the International Standard in immunogenicity assays as in antigenicity assays. On the other hand another vaccine, derived from the LEP strain, was considerably more potent in antigenicity assays than in immunogenicity assays. The glycoprotein of the proposed replacement standard measured in antigenicity assays appeared to be stable at +37 degrees C for 245 days, whereas the immunogenicity of the proposed replacement vaccine was sensitive to this heat treatment and the vaccine lost 66% of its immunogenic potency. The results of this study indicate that the NIH protection test should continue to form the primary basis for potency assay of rabies vaccine as glycoprotein content does not appear to correlate with immunogenic potency for different types of vaccine. The vaccine coded PISRAV has been established as the fifth International Standard for Rabies Vaccine and a potency of 16 International Units of Rabies Vaccine (based on the immunogenicity assays) assigned to the contents of each ampoule. Each ampoule has also been assigned a unitage of 10 IU of PM Rabies Virus Glycoprotein and 135 IU of PM Rabies Virus Ribonucleoprotein.

Animals↗
PubMed1983

Ligand/receptor internalization: a kinetic, flow cytometric analysis of the internalization of N-formyl peptides by human neutrophils.

Fluorescence flow cytometry was used to measure the internalization of the fluorescent ligand N-formyl-nle-leu-phe-nle-tyr-lys-fluorescein by human neutrophils. The internalization process was monitored by the accessibility of the receptor-bound fluorescent ligand to quenching following a change in the pH of the extracellular medium from 7.4 to 3.0. In such a pH change, extracellular ligand or fluorescein are quenched immediately (excitation 488 nm). In contrast, intracellular fluorescein (derived from fluorescein diacetate) or intracellular ligand are quenched with half-times of approximately 20 or approximately 40 sec, respectively, at 37 degrees C. The fraction of internalized ligand is calculated by resolving the fast and slow components of the quenching process. Temporal resolution of the internalization process in this system depends upon two factors. We have previously shown that it is possible to examine essentially continuously the kinetics of ligand binding in the nM concentration range without removing the free ligand (Sklar LA, Finney DA, Cytometry 3:161, 1982). We have now modified a Becton Dickinson FACS IV sample head assembly to permit direct addition of reagents into the cell suspension while on-line. This enables us to change the suspension pH and evaluate internalization with a time resolution of a few seconds. We observe that internalized ligand can be detected within 1 min and that the rate is proportional to the number of receptors occupied. The rate is essentially linear over the first few minutes and approximately 60% of the receptor-bound ligand is internalized after 3 min.

Flow Cytometry↗
PubMed1982

Ligand/receptor internalization: a spectroscopic analysis and a comparison of ligand binding, cellular response, and internalization by human neutrophils.

We have compared the kinetics of the responses of neutrophils to the kinetics of ligand-receptor interaction and internalization, using as a model ligand the fluoresceinated hexapeptide N-CHO-Nle-Leu-Phe-Nle-Tyr-Lys-Fluorescein (Nle, norleucine). Cellular responses, ie, membrane depolarization, enzyme (elastase) secretion, and superoxide anion (O-2) generation, are all initiated within 10 sec of the exposure of cells to stimulus. In the cases of membrane depolarization and secretion (in cytochalasin B-treated cells), full responses are elicited by binding which occurs within 15 sec of peptide addition. Ligand binding and internalization have been analyzed over the same time frame with new spectroscopic techniques. The association of ligand and receptor is monitored using an antibody to fluorescein. The antibody to fluorescein specifically quenches the ligand which is in solution, but receptor-bound ligand is inaccessible to the antibody. The internalization of the receptor-bound ligand is monitored by the accessibility of the fluoresceinated peptide to quenching by an external pH change (7.4 leads to 4.0). Ligand which is either outside or on the cell surface is instantaneously quenched while intracellular peptide (or intracellular fluorescein derived from fluorescein diacetate) is only slowly quenched. No internalization is observed until 1 min after binding begins and internalization proceeds at a rate of up to 5,000 receptors/min/cell following a near optimal stimulatory ligand concentration (approximately 1 nM) while the occupied receptors are being cleared from the surface. A comparison of the kinetics of internalization and the cellular responses suggests that internalization of the ligand is too slow to be involved in the triggering of the cellular responses.

Cell Membrane↗
PubMed1983

Internalization and recycling of plasma membrane glycoconjugates during pinocytosis in the macrophage cell line, P388D1. Kinetic evidence for compartmentation of internalized membranes.

An analysis was made of the pinocytosis-derived internalization and recycling of membrane in the macrophage cell line, P388D1. Plasma membrane glycoconjugates, reversibly labelled with [3H]galactose, were used as a membrane marker. Label internalized with the plasma membrane was no longer accessible to release by externally added beta-galactosidase and could therefore be distinguished quantitatively from label remaining on the cell surface. Direct experimental evidence for membrane recycling was obtained by demonstrating that previously internalized label reappeared at the cell surface. The composition of labelled membrane glycoconjugates, as analysed by SDS-polyacrylamide gel electrophoresis, remained unaltered before and after internalization. The label remained membrane-bound in an unmodified way during the entire period of 8 h investigated, corresponding to about twenty-four cycles of membrane flow. Membrane flow led to a steady-state distribution of label between the plasma membrane and intracellular membranes. The redistribution of label occurred with biphasic kinetics, which could be described as the sum of two exponential functions. This behavior is explained by presenting a model of membrane flow between the plasma membrane and two consecutive intracellular membrane compartments, which we assume to consist of pinosomal membranes and of pinosome-derived membrane of secondary lysosomes. The relative membrane surface areas turn out to be in the ratio of 100:12.5:7.3, respectively. At the observed rate of pinocytosis, the equivalent of the plasma membrane is internalized once every 21 min, in the form of primary pinosomes of the size 0.24 micrometer. The residence time of membranes in the pinosome compartment is about 3 min. The rate at which membranes enter the lysosomal compartment is 31 times lower than the rate of membrane internalization. We conclude that only 3% of the amount of membrane internalized at any one time subsequently enters the secondary lysosome compartment. After a residence time of 49 min this membrane fraction is finally recycled to the cell surface. The results are discussed in terms of mixing and sorting-out of pinosomal and lysosomal membranes.

Animals↗
PubMed1997

Ligand-induced internalization of cholecystokinin receptors. Demonstration of the importance of the carboxyl terminus for ligand-induced internalization of the rat cholecystokinin type B receptor but not the type A receptor.

Internalization of a variety of different heptahelical G protein-coupled receptors has been shown to be influenced by a number of different structural determinants of the receptors, including the carboxyl terminus. To investigate the role of the carboxyl terminus of cholecystokinin (CCK) receptors in receptor internalization, the rat wild type (WT) CCK-A receptor (WT CCKAR) and the rat WT CCK-B receptor (WT CCKBR) were truncated after amino acid residue 399 (CCKAR Tr399) and 408 (CCKBR Tr408), thereby deleting the carboxyl-terminal 45 and 44 residues, respectively. All WT and mutant CCK receptors were stably expressed in NIH/3T3 cells. Internalization of the CCKAR Tr399 was not significantly different from the WT CCKAR. In contrast, internalization of the CCKBR Tr408 was decreased to 26% compared with the WT CCKBR internalization of 92%. The mutation of all 10 serine and threonine residues (as potential phosphorylation sites) in the carboxyl terminus of the CCKBR to alanines (mutant CCKBR DeltaS/T) could account for the majority of this effect (39% internalization). All mutant receptors displayed similar ligand binding characteristics, G protein coupling, and signal transduction as their respective WT receptors, indicating that the carboxyl termini are not necessary for these processes. Thus, internalization of the CCKBR, unlike that of the CCKAR, depends on the carboxyl terminus of the receptor. These results suggest that, despite the high degree of homology between CCKAR and CCKBR, the structural determinants that mediate the interaction with the endocytic pathway reside in different regions of the receptors.

3T3 Cells↗
PubMed2000

GCP-2-induced internalization of IL-8 receptors: hierarchical relationships between GCP-2 and other ELR(+)-CXC chemokines and mechanisms regulating CXCR2 internalization and recycling.

The chemotactic potencies of ELR(+)-CXC chemokines during acute inflammation are regulated by their binding affinities and by their ability to activate, desensitize, and internalize their specific receptors, CXCR1 and CXCR2. To gain insight into the fine mechanisms that control acute inflammatory processes, we have focused in this study on the highly potent ELR(+)-CXC chemokine Granulocyte Chemotactic Protein 2 (GCP-2), and on its ability to control the cell surface expression of CXCR1 and CXCR2. Although GCP-2 has been considered an effective ligand for both CXCR1 and CXCR2, our findings demonstrated that it was a potent inducer of CXCR2 internalization only. A functional hierarchy was shown to exist between GCP-2 and 2 other ELR(+)-CXC chemokines, IL-8 and NAP-2, in their abilities to induce CXCR1 and CXCR2 internalization, according to the following: IL-8 > GCP-2 > NAP-2. By the use of pertussis toxin (PTx), it was demonstrated that the actual events of G(alphai)-coupling to CXCR2 do not have a major role in the regulation of its internalization. Rather, CXCR2 internalization was shown to be negatively controlled by induction of signaling events, as indicated by the promotion of CXCR2 internalization following exposure to wortmannin, a potent inhibitor of phosphatidylinositol (PI) 3 kinases and PI4 kinases. Furthermore, our results suggest that rab11(+)-endosomes participate in the trafficking of CXCR2 through the endocytic pathway, to eventually allow its recycling back to the plasma membrane. To conclude, our findings shed light on the interrelationships between GCP-2 and other ELR(+)-CXC chemokines, and determine the mechanisms involved in the regulation of GCP-2-induced internalization and recycling of CXCR2. (Blood. 2000;95:1551-1559)

Androstadienes↗
PubMed1992

Role of acidic subcellular compartments in the degradation of internalized insulin and in the recycling of the internalized insulin receptor in liver cells: in vivo and in vitro studies.

Upon interaction with liver cells, insulin is internalized along with its receptor into nonlysosomal endocytic structures termed endosomes. In this work, the biochemical evidence supporting the role of endosomal acidity in the degradation of internalized insulin and in the recycling of the internalized insulin receptor is described. Treatment of rats by chloroquine and/or quinacrine, two acidotropic drugs, increases by 5-10 fold the amount of endogenous insulin associated with endosomal fractions and, in rats injected by 125I-labeled or native insulin, the endosomal uptake of these ligands at late times after injection. With 125I-insulin, these drugs inhibit the degradation of internalized hormone as judged on physical, biological and immunological criteria. Chloroquine and quinacrine treatment also increases the insulin receptor content of endosomal fractions and, in rats injected by native insulin, the ligand-induced accumulation of receptors in endosomal fractions at late times after injection. Subfractionation of endosomal fractions on Percoll gradients shows that chloroquine treatment shifts the distribution of both insulin and the insulin receptor towards higher densities, the receptor shift being slightly more pronounced in insulin-injected rats. Incubation of isolated endosomes containing internalized insulin at 30-37 degrees C results in a rapid degradation of this ligand, with a maximal at pH 5-6. Addition of ATP, by decreasing the endosomal pH, stimulates insulin degradation above pH 7, whereas addition of chloroquine and quinacrine, by elevating endosomal pH, exerts opposite effects. These data indicate that endosomal acidity is required for optimum degradation of internalized insulin within endosomes and recycling of the internalized receptor.

Animals↗
PubMed1993

Clathrin-coated pit-mediated receptor internalization. Role of internalization signals and receptor mobility.

Most signals controlling receptor-mediated endocytosis have been identified by alteration of sequences present in receptors normally internalized via clathrin-coated pits. In the present work we have reconsidered the factors that control internalization the other way around: i.e. by introducing potential internalization sequences in complement receptor 1 (CR1) which does not preferentially associate with clathrin-coated pits. The analysis of the internalization efficiency of NPxY related motifs generated by substituting His2010 and/or Glu2015 by either Phe or Tyr indicates that FxNPxY is the stronger promoter of endocytosis and that the signal efficiency depends on the presence of aromatic residues (including a tyrosine) at both ends of the -xNPx- motif. Moreover, CR1-tyr (substitution of Glu2015 for Tyr) internalization was superposable to that of a receptor composed of the extracellular and transmembrane domains of CR1 fused to the intracytoplasmic tail of the low density lipoprotein (LDL) receptor (including the FxNPxY motif) (CR1-LDL). When analyzed by fluorescence recovery after photobleaching, the surface mobility of CR1-LDL was decreased as compared with that of either CR1-tyr or CR1-wt, despite a similar association with clathrin-coated pits. The role of receptor mobility in internalization was confirmed by the observation that CR1-tl, with a deletion of the cytoplasmic tail, was more mobile and more efficiently internalized than CR1-wt.

Amino Acid Sequence↗
PubMed1994

Characteristics of the internalization signal in the Y543 influenza virus hemagglutinin suggest a model for recognition of internalization signals containing tyrosine.

Several proteins, including the hemagglutinin (HA)-Y543 mutant influenza virus hemagglutinin, are internalized by clathrin-coated pits but do not have a sequence that fits a recently proposed consensus for internalization signals containing tyrosine. To determine whether or not the HA-543 signal is a degenerate form of the internalization signal found in proteins such as the transferrin receptor and mannose 6-phosphate/insulin-like growth factor (IGF) II receptor, we have mutated amino acid positions of HA-Y543 shown to be important for internalization of the two receptors. Our results indicate that the HA-Y543 mutant contains a sub-optimum sequence for a tyrosine-based internalization signal similar to those found in the receptors for transferrin, low density lipoprotein, and mannose 6-phosphate/IGFII. However, amino acids with side chains having very different chemical properties functioned well in positions that are important for the internalization signal. The variety of amino acid side chains found in known internalization sequences suggests that atoms of the polypeptide chain backbone may contribute important interactions for binding proteins to clathrin coats, with many of the side chains serving mainly to permit these interactions, a situation similar to that observed for the binding of peptides by histocompatibility proteins.

Amino Acid Sequence↗
PubMed1993

Contractility of the human internal mammary artery at the distal section increases toward the end. Emphasis on not using the end of the internal mammary artery for grafting.

The distal section of the internal mammary artery (3 to 4 cm proximal to the bifurcation) is often used for coronary grafting. This part of the artery is more pharmacologically responsive to vasoconstrictor agents than is its midsection. The present study was designed to test the hypothesis that the reactivity of the distal section of the internal mammary artery is inversely correlated to the diameter of the artery. The distal section of the human internal mammary artery was collected from aorta-coronary bypass grafts and studied in organ baths at a length of 3 mm. At the optimal point of the length-tension curves determined by a computer-iterative fitting technique, the diameter at 100 mm Hg, the maximal contraction forces and effective concentration causing 50% of the maximal response to vasoconstrictor agents U46619, potassium chloride, alpha-adrenoceptor agonists norepinephrine, methoxamine, and phenylephrine were recorded or calculated. The maximal relaxation and 50% response to glyceryl trinitrate in phenylephrine-precontracted internal mammary artery segments were also calculated. The contraction force was standardized by the circumference (grams per millimeter). Regression analysis between contraction force and diameter revealed that the contraction force induced by U46619 and potassium chloride was inversely correlated to diameter (r2 = 0.2, p < 0.05 in U46619-induced contraction and r2 = 0.2, p < 0.01 in potassium chloride-induced contraction). The contraction force induced by norepinephrine also had a trend inversely correlated to diameter (r2 = 0.2, p = 0.07). Glyceryl trinitrate-induced relaxation was not correlated to diameter. This study demonstrated that the contractility of the distal section of the internal mammary artery is inversely correlated to the diameter; that is, the smaller the diameter, the greater the tendency for spasm to develop. This suggests that trimming off the distal end of the internal mammary artery as much as possible may be the best way to prevent graft spasm and that superior results of left internal mammary artery grafted to the left anterior descending artery or the use of a "free graft" may be related to the shorter length (distal end is trimmed off) and less contractility of the graft.

Coronary Artery Bypass↗