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Biomedical subjects

Z Li

Publications and source records attributed to Z Li.

At least 1,369 records · Page 76Linked to original sources
PubMed1995

Plakoglobin: kinetics of synthesis, phosphorylation, stability, and interactions with desmoglein and E-cadherin.

We have analyzed the kinetics of synthesis, phosphorylation, and stability of the soluble and insoluble plakoglobin (PG) and their interactions with Dsg1 and E-cadherin in Madin-Darby canine kidney (MDCK) epithelial cells in the absence of cell adhesion and after the induction of cell-cell contact. Using a combination of biochemical and morphological approaches, we show that newly synthesized PG enters a soluble:insoluble pool of proteins in a 60:40 ratio regardless of cell-cell contact. Following synthesis, PG is increasingly found in the insoluble pool. Although cell-cell contact does not effect either the size of each pool or the rate or efficiency of the transfer from the soluble into the insoluble pool, it results in a significant increase in the metabolic stability of the newly synthesized insoluble PG. The soluble PG initially forms separate complexes with E-cadherin and Dsg1. PG-Dsg1 complexes become insoluble and localize to the desmosome. PG-E-cadherin complexes remain soluble and are distributed intracellularly. The insoluble PG and E-cadherin detected at the cell periphery remain distinctly separate, as demonstrated previously [Hinck et al., 1994: J. Cell Biol. 125:1327-1340; Nathke et al., 1994: J. Cell Biol. 125:1341-1352]. In addition, we detected a separate pool of PG which is not associated with either Dsg1 or E-cadherin and after the induction of cell-cell contact becomes primarily insoluble and is distributed along the lateral membrane. Phosphorylation analysis showed that there is a significantly greater amount of phosphorylated PG in the soluble pool than in the insoluble pool. In addition the soluble pool is both serine and threonine phosphorylated, whereas the insoluble PG is primarily phosphorylated on serine residues.

Animals↗
PubMed1995

Solid-phase fluorescent labeling reaction of picomole amounts of insulin in very dilute solutions and their analysis by capillary electrophoresis.

The fluorescent labeling of peptides at concentrations as low as 10(-8) M can be achieved by using a solid-phase reactor. Using oxidized insulin chain B as a test peptide, we demonstrate the use of an Immobilon CD membrane to capture and preconcentrate peptides. Insulin chain B can then be labeled with a fluorogenic reagent, 3-(2-furoyl)quinoline-2-carboxaldehyde, while it is still attached to the membrane. Unwanted fluorescent products (attributed to secondary reactions) can be washed away with methanol without significant removal of the labeled insulin chain B, which then can be extracted with a low pH buffer. The analysis by micellar electrokinetic capillary chromatography with post-column laser-induced fluorescence detection (mass limit of detection of 2.4 x 10(-21) moles insulin chain B) results in electropherograms that show great improvement in terms of unwanted peaks and high number of theoretical plates (up to 20 million). The use of the solid-phase reactor allows easy handling of as little as 5 picomoles of insulin chain B.

Animals↗
PubMed1995

Mitogenic factors released from smooth muscle cells are responsible for neointimal cell proliferation after balloon catheter deendothelialization.

Smooth muscle cell (SMC) proliferation results in neointimal formation in response to selective deendothelialization. The neointimal SMC are characteristically different from normal, medial SMC. The major difference is that neointimal SMC have a higher proliferation rate. The high proliferation rate has been observed 15 weeks after endothelial injury. In this study, it is noted that neointimal SMC release some mitogenic factor(s) which is(are) responsible for inducing persistent SMC proliferation in an autocrine manner. The SMC were cultured from the media of normal rabbit aorta as well as the neointimal tissue formed 15 weeks after an endothelial injury. From the culture of the neointimal SMC, the conditioned medium was collected and growth factors, including PDGF-AB, TGF-beta 1, TGF-beta 2, and bFGF, were assayed. The conditioned medium was used to culture the medial SMC from normal rabbit aorta. The mitogenic effect of the conditioned medium was evaluated by the incorporation of [3H]thymidine into the SMC. Results demonstrated that PDGF-AB and TGF-beta 1 were increased in neointimal SMC-conditioned medium. After incubation with the conditioned medium, medial SMC incorporated significantly higher [3H]thymidine, compared to incubation with control medium (P < 0.01). The data indicate that endothelial injury induces production of some growth factors, including PDGF and TGF-beta, by the neointimal SMC. These growth factors may act in an autocrine manner to stimulate SMC proliferation for a long time following a single deendothelialization.

Animals↗
PubMed1995

Pyrophosphate-dependent phosphofructokinase from Giardia lamblia: purification and characterization.

The pyrophosphate-dependent phosphofructokinase (EC 2.7.1.90) from Giardia lamblia has been purified to homogeneity using two methods. The purified enzyme is shown to be homogenous by its migration as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and a single peak on reverse-phase HPLC. The purified enzyme is a monomeric protein of Mr 64 kDa as determined by SDS-PAGE and native PAGE. The enzyme fractionated as a 67-kDa protein by HPLC gel filtration. The pH optima in either the glycolytic or the gluconeogenic direction is near neutral, which is unlike any of the protozoan or bacterial enzymes. The enzyme displayed typical Michaelis-Menten kinetics. The Km values for pyrophosphate and fructose 6-phosphate were 0.039 +/- 0.005 and 0.25 +/- 0.0196 mM, respectively. The initial velocity for the reverse reaction was also found to be hyperbolic. Different nucleoside triphosphates, including ATP, could not substitute for pyrophosphate as the phosphoryl donor. Similar to the pyrophosphate-dependent enzyme from other anaerobic protozoans and bacteria, the Giardial enzyme was not activated by fructose 2,6-bisphosphate, although this metabolite is a competitive inhibitor with respect to fructose 1,6-bisphosphate in the reverse reaction. The pH optima and the molecular weight properties of the Giardial enzyme are different from those of the two classes of the pyrophosphate-dependent phosphofructokinases.

Animals↗
PubMed1995

Purification, properties, and immunological characterization of GalT-3 (UDP-galactose: GM2 ganglioside, beta 1-3 galactosyltransferase) from embryonic chicken brain.

A beta 1-3 galactosyltransferase (GalT-3; UDP-Gal; GM2 beta 1-3 galactosyltransferase) was purified over 5100-fold from 19-day-old embryonic chicken brain homogenate employing detergent solubilization, alpha-lactalbumin Sepharose, Q-Sepharose, UDP-hexanolamine Sepharose, and GalNAc beta 1-4Gal beta-Synsorb column chromatography. The purified enzyme was resolved into two bands on reducing gels with apparent molecular weights of 62 kDa and 65 kDa, respectively. GalT-3 activity was also localized in the same regions by activity gel analysis and sucrose-density gradient centrifugation of a detergent-solubilized extract of 19-day-old embryonic chicken brain. Purified GalT-3 exhibited apparent Kms of 33 microM, and 14.4 mM with respect to the substrates GM2, UDP-galactose, and MnCl2, respectively. Substrate specificity studies with the purified enzyme and a variety of glycosphingolipids, glycoproteins, and synthetic substrates revealed that the enzyme was highly specific only for the glycosphingolipid acceptors, GM2 and GgOse3Cer (asialo-GM2). Ovine-asialo-agalacto submaxillary mucin inhibited the transfer of galactose to GM2 but did not act as an acceptor in the range of concentrations tested. Polyclonal antibodies raised against purified GalT-3 inhibited GalT-3 activity in vitro and Western-immunoblot analysis of purified GalT-3 showed immunopositive bands at 62 and 65 kDa.

Animals↗
PubMed1995

Correlation of DNA fragment sizes within loci in the presence of non-detectable alleles.

At present most forensic databases of DNA profiling of individuals consist of DNA fragment sizes measured from Southern blot restriction fragment length polymorphism (RFLP) analysis. Statistical studies of these databases have revealed that, when fragment sizes are measured from RFLP analysis, some of the single-band patterns of individuals may actually be due to heterozygosity of alleles in which fragment size resulting from one allele remains undetected. In this work, we evaluate the effect of such allelic non-detectability on correlation of fragment sizes within individuals at a locus, and its impact on the inference of independence of fragment sizes within loci. We show that when non-detectable alleles are present in a population at a locus, positive correlations of fragment sizes are expected, which increase with the proportion of non-detectable alleles at the locus. Therefore, a non-zero positive correlation is not a proof of allelic dependence within individuals. Applications of this theory to the current forensic RFLP databases within the US show that there is virtually no evidence of significant allelic dependence within any of the loci. Therefore, the assumption that DNA fragment sizes within loci are independent is valid, and hence, the population genetic principles of computing DNA profile frequencies by multiplying binned frequencies of fragment sizes are most likely to be appropriate for forensic applications of DNA typing data.

Alleles↗
PubMed1995

Functional bowel disorders. A multicenter comparison of health status and development of illness severity index.

In a multicenter study of patients with painful functional bowel disorders (FBD), we compared the demographic, health status, and diagnostic features of patients with FBD and developed a functional bowel disorder severity index (FBDSI) for research and clinical care. Two hundred seventy patients with FBD in the United States, England, and Canada were surveyed on symptoms and health status, and their physicians made a diagnosis and rated illness severity as mild, moderate, or severe. Comparisons of 22 demographic and clinical variables were made by study site in addition to physicians' severity ratings. To develop the FBDSI, multiple regression analysis used the demographic and clinical variables to predict the physician's rating of severity. We found that most health status measures of patients with FBD across study sites are comparable and the derived and validated FBDSI scoring system uses three easy to obtain variables: FBDSI = [current pain by visual analog scale (0-100)] + [diagnosis of chronic functional abdominal pain (0 if absent and 106 if present)] + [number of physicians visits over previous six months x 11]. The FBDSI can be used to select patients for research protocols and/or follow their clinical outcome or response to treatments over time.

Abdominal Pain↗
PubMed1995

Guanylin, an endogenous ligand for C-type guanylate cyclase, is produced by goblet cells in the rat intestine.

BACKGROUND & AIMS: Guanylin activates an intestinal guanylate cyclase (GCC) and stimulates electrolyte movement across the gut epithelium. Cells expressing guanylin messenger RNA have been localized to the epithelial cell layer of the intestine; however, the identity of the guanylin-producing cells has not been determined. The aim of this study was to identify cells that express guanylin in the rat intestine. METHODS: Antibodies were raised against defined proguanylin epitopes, evaluated by Western blotting, and used for immunoperoxidase histochemistry. RESULTS: Guanylin-like immunoreactivity was localized to a subset of goblet cells. In the small intestine, most, perhaps all, goblet cells in the villi were immunopositive, as were some goblet cells in upper crypts; however, goblet cells deep within crypts were unlabeled. In the colon, goblet cells clustered in the necks and around the openings of crypts were immunopositive, whereas (as in the small intestine) goblet cells in deeper crypt regions were unlabeled. In some animals, immunoreactive columnar epithelial cells were also observed in the colon (although such cells were not apparent in the small intestine). Relative labeling of columnar cells varied from animal to animal. CONCLUSIONS: Guanylin is expressed in mature goblet cells. If secreted in conjunction with mucin, it could play a role in the hydration of mucus.

Animals↗
PubMed1995

Dynamic behavior of a biphasic cartilage model under cyclic compressive loading.

It is well known that dynamic mechanical loads can stimulate the biosynthetic activity of articular cartilage. Studying the mechanical environment of chondrocytes under dynamic loading conditions can help to explain this mechano-biological phenomenon in articular cartilage. In this study, the linear biphasic theory was used to examine the dynamic mechanical behavior of articular cartilage under a cyclic compressive force. We first studied the dynamic confined compression of a cartilage disk as a simplified one-dimensional model and then investigated the role of the relatively impermeable subchondral bone structure on the dynamic behavior of the cartilage extracellular matrix (ECM). Under an assumption of articular cartilage as a biphasic composite structure of a porous elastic solid matrix and interstitial fluid, the porous ECM of the articular cartilage was repeatedly compressed and expanded during the loading-unloading phases of the cyclic compressive force. One interesting finding of this study was the oscillating positive (supra-ambient)-negative (sub-ambient) hydrostatic pressure within the cartilage ECM under cyclic compressive loading. The pattern of the dynamic behavior of the cartilage ECM strongly depended on the loading frequency and the primary diffusion characteristic time, tau d. This finding is consistent with those of previous studies (Guilak et al., 1990 Adv Biomech. ASME, 225-228; Mow et al., 1990, Biomechanics of Diarthrodial Joints, pp. 215-260.

Algorithms↗
PubMed1995

Kinetic mechanism of pyrophosphate-dependent phosphofructokinase from Giardia lamblia.

The steady-state kinetics of the reaction catalyzed by inorganic-pyrophosphate-dependent D-fructose-6-phosphate 1-phosphotransferase from Giardia lamblia have been investigated. The reactants for the forward and reverse reactions were the Mg-chelated complexes of pyrophosphate (PPi) and Pi. Uncomplexed ligands were not substrates. In the direction of phosphorylation of fructose-6-phosphate (F6P), initial velocity double-reciprocal plots for both PPi and F6P were intersecting suggesting sequential addition of substrates. Similarly, intersecting patterns were observed in the reverse reaction with either Pi or fructose-1,6-bisphosphate (FBP) as the variable substrate. Although the catalytic constants for the forward and reverse reactions were found to be identical (83 s-1), the kcat/Km for PPi is about two orders of magnitude higher than the kcat/Km for Pi, indicating that PPi is utilized much more efficiently than Pi. Product inhibition of Pi is competitive vs. PPi and noncompetitive vs. F6P, when the fixed substrate is subsaturating. Product inhibition by FBP was found to be noncompetitive with either Pi or F6P as the variable substrate. These results are consistent with a sequential ordered Bi Bi mechanism with PPi adding first and Pi dissociating last. In the reverse reaction, however, PPi and F6P were found to be noncompetitive with either Pi or FBP. Dead-end inhibition analysis with fructose 2,6-bisphosphate, a competitive substrate analog of FBP, gave uncompetitive inhibition with respect to Pi, indicating that fructose 2,6-bisphosphate (and hence FBP) binds after Pi. This kinetic mechanism is different from that observed with the enzyme from Propionibacterium freudenreichii, Entamoeba histolytica or Mung bean, which were concluded to be rapid equilibrium random mechanism.

Animals↗
PubMed1995

Calpain as a novel target for treating acute neurodegenerative disorders.

Calpains are cytosolic, neutral proteases that normally exist in an inactive or quiescent state. They require higher than normal levels of calcium for activation which, once accomplished, lead to irreversible proteolysis of numerous cytoskeletal, membrane-associated and regulatory proteins. Because of these characteristics, calpain is gaining attention as a potentially important pathogenic variable in ischemic neuronal death. This manuscript explores this hypothesis by briefly reviewing current support for the role played by calpain in ischemic neurodegeneration, and then discussing a series of recently published studies which: 1. offer further evidence for the hypothesis, and 2. provide direct support for the idea that selective inhibition of calpain can greatly limit the neuronal damage that would normally occur following both global as well as focal brain ischemia. Thus, the data reviewed in this manuscript support the ideas that unregulated activation and proteolysis of intraneuronal calpain plays a significant role in the brain damage that occurs following an ischemic event and that delivering selective and membrane permeant calpain inhibitors to ischemic tissue may provide a powerfully effective therapeutic means of limiting neuronal damage.

Animals↗
PubMed1995

The reliability and validity of a sexual and physical abuse history questionnaire in female patients with gastrointestinal disorders.

Although the literature on the psychological and medical sequelae of sexual and physical abuse has been growing, researchers have made few attempts to standardize the measurement of abuse history. The authors of this article report the first standardization of a screening instrument to identify sexual and physical abuse in a medical population. Reliability was assessed using test-retest methodology, and validity was supported by comparison with an interview (criterion validity). The sample included 139 female patients in a gastroenterology clinic. Data indicate acceptable test-retest reliability of the sexual abuse instrument (81%) and 81% overall agreement between the questionnaire and the interview on any sexual abuse. In comparison, the authors found 77% agreement in test-retest reliability of the physical abuse questionnaire and 70% agreement between the questionnaire and the interview on physical abuse. From their analyses, they concluded that the sexual abuse questionnaire and, to a lesser extent, the physical abuse instrument have acceptable levels of reliability and validity. As a screening tool, the abuse measures could be used to identify women in clinic settings for further study.

Adult↗
PubMed1995

Cardiac sodium channel mutations in patients with long QT syndrome, an inherited cardiac arrhythmia.

Long QT syndrome (LQT) is an inherited cardiac disorder that causes syncope, seizures and sudden death from ventricular tachyarrhythmias. We used single-strand conformation polymorphism (SSCP) and DNA sequence analyses to identify mutations in the cardiac sodium channel gene, SCN5A, in affected members of four LQT families. These mutations include two identical intragenic deletions and two missense mutations. These data suggest that SCN5A mutations cause LQT. The location and character of these mutations suggest that this form of LQT results from a delay in cardiac sodium channel fast inactivation or altered voltage-dependence of inactivation.

Amino Acid Sequence↗
PubMed1995

Preferential recognition by human IgE and IgG4 of a species-specific Schistosoma haematobium serine protease inhibitor.

IgE induction in schistosomiasis is an important human response to infection, yet few specific parasite allergens have been characterized. One allergen of Schistosoma haematobium was found to be a species-specific surface antigen and a member of the serine protease inhibitor gene family (SH serpin). The purified recombinant SH serpin protein was used to characterize human isotypic responses to this antigen. Quantitative ELISA based on the recombinant antigen revealed marked IgG4 and IgE responses and a high degree of species specificity (IgG = 96%, IgG4 = 66%, and IgE = 95%) in sera from S. haematobium-infected persons. In contrast, ELISA based on soluble adult worm or egg antigens could not discriminate between species. There was no correlation between serpin-specific IgE and IgG4 levels in 41 infected persons. Further, serpin-induced antibody production in vitro indicated that IgE and IgG4 responses are not coordinately regulated.

Adolescent↗