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Biomedical subjects

A Taylor

Publications and source records attributed to A Taylor.

At least 469 records · Page 26Linked to original sources
PubMed1993

Cataract incidence and analysis of lens crystallins in the water-, urea- and SDS-soluble fractions of Emory mice fed a diet restricted by 40% in calories.

Restriction of dietary calorie intake is associated with life extension and with the delay of age-related disorders. Preliminary studies demonstrated that by feeding the Emory mouse a diet restricted by 21% in calories cataract and insolubilization of protein could also be delayed. To observe the effects of calorie restriction over prolonged portions of adulthood, Emory mice were fed the control diet (C) or a diet restricted by 40% in calories (R). Feeding the R diet was associated with delayed formation or progress of cataract over virtually the entire second half of life. At 11 months of age, bilateral grade 5 cataracts were present in 17% and 2% of C and R lenses, respectively. At 22 months of age, bilateral grade 5 cataracts were present in 90% and 18% of C and R lenses, respectively. The distribution of alpha-, beta-, and gamma- crystallins in the water-soluble, urea-soluble, and SDS-soluble fractions indicates more similarities than differences between C and R lenses with a specific grade of cataract or of a given age. However, there were significant and abrupt (after grade 4 cataract) losses of particular gamma-crystallins; gamma-crystallins which were not prominent at earlier stages became the major gamma-crystallin moieties. Losses of alpha-crystallins were also noted upon cataract formation or aging in most of the fractions. Aggregates including gamma- and alpha-crystallins also accumulate faster in the C group.

Aging↗
PubMed1993

Aminopeptidases: towards a mechanism of action.

Aminopeptidases catalyse the removal of amino acids from peptide substrates. Although many functions have been ascribed to these enzymes, lack of knowledge of their complex structure has prevented detailed analysis. Several recent studies have now provided information on the structure and molecular biology of these enzymes, the kinetics of substrate hydrolysis and inhibitor binding. These new data allow prediction of a model mechanism of action for a large subgroup of aminopeptidases.

Aminopeptidases↗
PubMed1993

Evaluation of biomatrix hydroxyapatite ocular implants with technetium-99m-MDP.

Hydroxyapatite ocular implants appear to offer excellent cosmetic reconstruction with lower rates of infection and extrusion compared to other integrated implants. However, vascularization of the implant needs to be established before the artificial eye is attached to the implant. Technetium-99m-methylene diphosphonate (MDP) scintigraphy can be utilized as a noninvasive method for determining the vascularity of the hydroxyapatite ocular implants. A case is presented in which 99mTc-MDP uptake in the implant was deemed sufficient for further surgical intervention.

Durapatite↗
PubMed1993

Improved formulas for the estimation of renal depth in adults.

Commercial techniques are available to calculate effective renal plasma flow (ERPF) or glomerular filtration rate (GFR) based on the percent injected dose in the kidney 1-2 or 2-3 min post-injection; renal depth is estimated by the Tonnesen equations. Since the Tonnesen equations were derived from ultrasound measurements obtained at an oblique angle in sitting patients, we compared the renal depths obtained from the Tonnesen equations with the renal depth measured by computed tomography in supine patients, the most common position for radionuclide renography. The renal depth, height, weight, age and sex were determined for 126 patients undergoing CT scanning. Patients with obvious renal or abdominal pathology were excluded. The Tonnesen equations significantly underestimated renal depth. Using stepwise linear regression analysis, we derived a set of equations based on age, height and weight and applied these prospectively to a new set of 75 patients. In addition, a second set of equations were derived for the new data. There was no difference in the results for the two equations. We then pooled both studies and derived a combined set of equations: right renal depth (mm) = 153.1 weight/height + 0.22 age + 0.77 and left renal depth (mm) = 161.7 weight/height + 0.27 age - 9.4, where weight is in kilograms and height is in centimeters. The correlation coefficients were 0.81 and 0.83 for the right and left kidneys respectively with standard errors of the estimate of 10.2 and 10.1 mm. These equations provide a much better estimate of renal depth in the supine patient than the Tonnesen equations.

Female↗
PubMed1992

Novel antagonists of the 5-HT3 receptor. Synthesis and structure-activity relationships of (2-alkoxybenzoyl)ureas.

A series of benzoylureas derived from bicycle amines were prepared and evaluated for 5-HT3 antagonist activity on the rat isolated vagus nerve. From among these compounds, those analogues which were ortho substituted by an alkoxy group on the benzoyl function were shown to be potent 5-HT3 antagonists with similar or greater potency than the standard agent ondansetron. NMR and X-ray crystallography studies showed these o-alkoxy compounds to exist as a planar, hydrogen-bonded, tricyclic ring system. In molecular modeling studies on endo-N-[[(8-methyl-8-azabicyclo[3.2.1]octan-3-yl-amino] carbonyl]-2-(cyclopropylmethoxy)benzamide (30) the central hydrogen-bonded ring was able to mimic an aromatic ring present in previously reported 5-HT3 antagonists.

Animals↗
PubMed1992

Use of azidobestatin as a photoaffinity label to identify the active site peptide of leucine aminopeptidase.

Aminopeptidases catalyze the hydrolysis of amino acid residues from the amino terminus of peptide substrates. They are found in most cells and tissues, and their activity has been implicated in myriad fundamental biochemical and physiological processes. Nevertheless, little is known about the structure of the aminopeptidase active sites. Beef lens leucine aminopeptidase (blLAP) can be considered prototypical of many enzymes in this family of peptidases. Bestatin, [(2S,3R)-(3-amino-2-hydroxy-4-phenyl-butanoyl)-L-leucine] is a nonhydrolyzable substrate analogue of a peptide, PheLeu, which is rapidly cleaved by blLAP. Bestatin incorporates elements of the putative tetrahedral intermediate, and this results in a greater than 10(5)-fold enhancement of binding relative to analogous peptides. Bestatin is the most tightly bound inhibitor of many aminopeptidases. Bestatin was successively converted to nitrobestatin, p-aminobestatin, [3H]-p-aminobestatin, and finally [3H]-p-azidobestatin (pAB). Like bestatin, pAB is a slow binding inhibitor of LAP (Ki*, the dissociation constant for the final complex, = approximately 4 x 10(-9); Ki, the dissociation constant for the initial collision complex, = approximately 10(-8). The t1/2 for binding of 2 x 10(-8) M and 8 x 10(-8) M bestatin are approximately 60 min and approximately 38 min, respectively. pAB, nitrobestatin, bestatin, and physiological peptides appear to bind in the same site, the first three with similar avidity. In the dark, pAB and bestatin protect low concentrations of the enzyme against inactivation upon extensive dialysis. The t1/2 for photoactivation of pAB is approximately 3 s. Irradiation of blLAP for such short periods of time resulted in insignificant change in activity. blLAP which was placed in 254-nm light in the presence of pAB was inactivated significantly. Treatment of photolabeled blLAP with trypsin produces only two peptides. Autoradiography and scintillation counting indicate that the active site is in the peptide which includes residues 138-487. Treatment of the same blLAP with hydroxylamine produces two different peptides, with the active site in the peptide 323-487. This indicates that the active site is in the carboxyl-terminal one-third of the protomer. It is likely that this photoaffinity label will be useful in identifying active sites in other aminopeptidases as well.

Affinity Labels↗
PubMed1992

Organization of the human T cell receptor zeta/eta gene and its genetic linkage to the Fc gamma RII-Fc gamma RIII gene cluster.

The zeta-subunit is the most recently characterized stoichiometric human TCR component. In this study we describe the molecular organization of the human zeta-gene. The zeta transcript is generated as the spliced product of eight exons that are separated by distances of 0.7 kb to more than 8 kb. Ribonuclease protection studies revealed multiple transcription initiation sites distributed over a range of approximately 115 bases. A variable number tandem repeat restriction fragment polymorphism contained within the structural gene has allowed for the localization of zeta within the human genome. Additionally, a restriction fragment polymorphism within the Fc gamma RII-Fc gamma RIII gene cluster has allowed for its localization on the map of human chromosome 1q and for the establishment of its linkage to the zeta-gene locus. A region that is highly homologous on a nucleotide level with the eta-exon of the murine zeta-gene is localized to the 3' region of the human zeta-gene. Surprisingly, translation of this region into protein results in a structure that is markedly divergent from its murine counterpart. This finding has important implications regarding the potential role of eta in T cell function.

Amino Acid Sequence↗
PubMed1992

Induction of leucine aminopeptidase by interferon-gamma. Identification by protein microsequencing after purification by preparative two-dimensional gel electrophoresis.

The protein previously called "Mr approximately 50/pI approximately 6.9," which we observed to be induced by the immunoregulatory cytokine interferon (IFN)-gamma in human fibroblasts, was purified from a total cell lysate by preparative two-dimensional gel electrophoresis and identified by partial amino-terminal sequencing as leucine aminopeptidase (LAP), a 53-kDa cytosolic exopeptidase. Induction of LAP protein by IFN-gamma, confirmed by immunoblotting with an antiserum raised against bovine lens LAP, is a consequence of induction of LAP mRNA and occurs in all four human cell lines examined: HS153 fibroblasts, ACHN renal carcinoma, A549 lung carcinoma, and A375 melanoma. Induction of LAP mRNA is a secondary response to IFN-gamma, blocked by inhibition of protein synthesis with cycloheximide.

Amino Acid Sequence↗
PubMed1992

Structure determination and refinement of bovine lens leucine aminopeptidase and its complex with bestatin.

The three-dimensional structure of bovine lens leucine aminopeptidase (EC 3.4.11.1) complexed with bestatin, a slow-binding inhibitor, has been solved to 3.0 A resolution by the multiple isomorphous replacement method with phase combination and density modification. In addition, this structure and the structure of the isomorphous native enzyme have been refined at 2.25 and 2.32 A resolution, respectively, with crystallographic R-factors of 0.180 and 0.159, respectively. The current structural model for the enzyme includes the two zinc ions and 481 of the 487 amino acid residues comprising the asymmetric unit. The enzyme is physiologically active as a hexamer, which has 32 symmetry, and is triangular in shape with a triangle edge length of 115 A and maximal thickness of 90 A. Monomers are crystallographically equivalent. Each is folded into two unequal alpha/beta domains connected by an alpha-helix to give a comma-like shape with approximate maximal dimensions of 90 A x 55 A x 55 A. The secondary structural composition is 35% alpha-helix and 23% beta-strand. The N-terminal domain (160 amino acid residues) mediates trimer-trimer interactions and does not appear to participate directly in catalysis, while the C-terminal domain (327 amino acid residues) is responsible for catalysis and binds the two zinc ions, which are less than 3 A apart. These two metal ions are located near the edge of an eight-stranded, saddle-shaped beta-sheet. The zinc ion that has the lower temperature factor is co-ordinated by one carboxylate oxygen atom from each of Asp255, Asp332 and Glu334, and the carbonyl oxygen of Asp332. The other zinc ion, presumed to be readily exchangeable, is co-ordinated by one carboxylate oxygen atom of each of Asp273 and Glu334 and the side-chain amino group of Lys250. The active site also contains two positively charged residues, Lys262 and Arg336. The six active sites are themselves located in the interior of the hexamer, where they line a disk-shaped cavity of radius 15 A and thickness 10 A. Access to this cavity is provided by solvent channels that run along the 2-fold symmetry axes. Bestatin binds to one of the active site zinc ions, and its phenylalanine and leucine side-chains occupy hydrophobic pockets adjacent to the active site. Finally, the relationship between bovine lens leucine aminopeptidase and the homologous enzyme pepA from Escherichia coli is discussed.

Amino Acid Sequence↗
PubMed1992

Hypothalamic-pituitary function during alcohol exposure and withdrawal and cocaine exposure.

This chapter examines the neuroendocrine effects of acute exposure to and withdrawal from alcohol and cocaine, with special emphasis on the hypothalamic-pituitary-adrenal (HPA) axis. We present the results from two preliminary controlled inpatient studies that document HPA dysfunction during acute exposure to alcohol and cocaine and during withdrawal from alcohol. We discuss the methodological approach of these studies in comparison to related attempts in the literature to use measures of thyroid and prolactin regulation to predict risk of relapse to alcohol and cocaine use, respectively. Our data and the results of related studies are presented in the context of a proposed index of HPA axis dysfunction that may provide a useful clinical measure of susceptibility to relapse during protracted abstinence from alcohol or cocaine.

Adrenocorticotropic Hormone↗
PubMed1992

Effect of photooxidation on the eye lens and role of nutrients in delaying cataract.

The function of the eye lens is to collect and focus light on the retina. To do so, it must remain clear during the decades of life. Upon aging, lens constituents are damaged and precipitate in opacities called senile cataracts. Laboratory and epidemiologic data indicate that the damage is due in part to light and active forms of oxygen. Antioxidant nutrients - ascorbate, carotenoids, and tocopherol - appear to offer protection against cataract. Fifty million persons worldwide are blind due to cataract, and, in the U.S., there are 1.2 million cataract surgeries performed at an annual cost (including physician visits) of over $3.2 billion. It has been estimated that a 10-year delay in the development of cataract would eliminate the need for half the surgeries. Since it will not be possible to replace most of the damaged lenses, it is essential to determine the efficacy of supplying adequate levels of antioxidant nutrients early in life to preserve lens function.

Aging↗
PubMed1992

High-level expression and purification of mature HIV-1 protease in Escherichia coli under control of the araBAD promoter.

A 1.3-kb segment of Escherichia coli DNA containing the regulatory gene, araC, and the promoter of the araBAD operon was amplified by the polymerase chain reaction (PCR) and cloned into pUC18, resulting in plasmid pKB130 that produced the alpha fragment of beta-galactosidase upon addition of L-arabinose (L-ara). A synthetic gene for human immunodeficiency virus (HIV)-1 preprotease was placed downstream of the ara-BAD promoter in pKB130 to create a translational fusion inducible by addition of L-ara. The fusion protein correctly autoprocessed in vivo to yield a mature 99-amino-acid HIV-1 protease, which was found predominantly in inclusion bodies. This material could be refolded to an active form, which was purified to homogeneity. A small fraction of the protease was expressed in vivo as a soluble active form, which allowed the monitoring of expression during fermentation by a rapid and simple whole cell assay employing an HIV-1 protease-specific fluorogenic substrate.

Amino Acid Sequence↗
PubMed1992

Mutational analysis of SRY: nonsense and missense mutations in XY sex reversal.

XY females (n = 17) were analysed for mutations in SRY (sex-determining region Y gene), a gene that has recently been equated with the testis determining factor (TDF). SRY sequences were amplified by the polymerase chain reaction (PCR) and analysed by both the single strand conformational polymorphism assay (SSCP) and DNA sequencing. The DNA from two individuals gave altered SSCP patterns; only these two individuals showed any DNA sequence variation. In both cases, a single base change was found, one altering a tryptophan codon to a stop codon, the other causing a glycine to arginine amino acid substitution. These substitutions lie in the high mobility group (HMG)-related box of the SRY protein, a potential DNA-binding domain. The corresponding regions of DNA from the father of one individual and the paternal uncle of the other, were sequenced and found to be normal. Thus, in both cases, sex reversal is associated with de novo mutations in SRY. Combining this data with two previously published reports, a total of 40 XY females have now been analysed for mutations in SRY. The number of de novo mutations in SRY is now doubled to four, adding further strength to the argument that SRY is TDF.

Base Sequence↗
PubMed1992

Ubiquitin and ubiquitin conjugates in human lens.

Ubiquitin, an 8.5 kDa polypeptide found almost universally in plants and animals, is a normal component in the lens. The best documented function for ubiquitin involves its conjugation to proteins as a signal to initiate degradation. Conjugates for ubiquitin-dependent degradation tend to be of very high molecular mass and are rapidly degraded. Another role of ubiquitin conjugation may be as a stabilizer during stress for protection of constituent proteins, resulting in ubiquitin conjugates that are long-lived. Examination of clear and cataractous human lenses of < 1 to > 50 years revealed the dramatic accumulation of ubiquitin and ubiquitin conjugates with age, beginning at approximately 10 years. Epithelial tissue contained predominantly conjugates of > 250 kDa, although ubiquitin conjugates were found at 98 and 40-60 kDa in tissues from older donors. The water-soluble, urea-soluble and urea-insoluble fractions of lens cortex and core also contain ubiquitin conjugates that accrue with age. High molecular mass conjugates (> 250 kDa) are particularly prominent in older lens tissue. Cataractous lenses, as compared with normal lenses of the same age, show more of these high molecular mass conjugates in the urea-soluble and urea-insoluble fractions of cortex and core. Heterogeneous conjugates in the 20-85 kDa range accumulate in an age-related fashion in all lens cortex and core fractions. While levels of free ubiquitin are significant in the epithelium and the water-soluble cortex and core for all ages, there is no detectable free ubiquitin in the urea-soluble and urea-insoluble fraction under conditions used in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1992

Effect of a means-end contingency on young children's food preferences.

This study showed that a means-end relationship between two snacks exerts a negative influence on preference for the means snack in the contingency. Two snacks ranked of approximately equal medium appeal were individually chosen from an array by each of 86 children (ages 4 years, 4 months to 7 years, 2 months). Children were then assigned to a means-end condition (where one snack was eaten as a means of gaining the other), a temporal order control group (where one snack was presented and eaten before the other), or a mere exposure control group (where the children chose the order in which they ate the two snacks). Post-treatment rankings of the snacks showed that children in the means-end group came to devalue the means snack relative to the reward snack, despite the demonstrably equal prior appeal of the two snacks. Children in the temporal order and mere exposure control groups did not come to prefer the two snacks preferentially. Implications of the finding that adults can affect children's preferences by relatively minor variations in the manner of presentation are discussed.

Adolescent↗