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Biomedical subjects

G Avigad

Publications and source records attributed to G Avigad.

At least 19 recordsLinked to original sources
PubMed1988

Isolation and partial characterization of collagen chains dimerized by sugar-derived cross-links.

Incubation of tail tendon from a young rat in solutions containing D-ribose resulted in attachment of the monosaccharide to collagen and subsequent cross-link formation at a rate much faster than found for glucose. The collagen rapidly became resistant to solubilization and showed increasing fluorescence. Ribose bound to all major CNBr peptides of collagen, with some preference for the alpha 2-CB3,5 peptide and the triple-helical region of alpha 1-CB6, and was incorporated into higher molecular weight material. Extensive pepsin digestion permitted isolation of dimers of alpha chains cross-linked in triple-helical regions as a result of incubation with ribose. The dimers were identified as beta 11, beta 12, and beta 22 components, and the limited degree of heterogeneity of these components indicated that cross-linking occurred at several sites, some of which must be intermolecular. Isolated beta components were strongly fluorescent with a spectrum similar to that of collagen in aged tissues. Fluorescent dimers with similar characteristics were found in pepsin digests of tail tendons from older rats.

Animals↗
PubMed1988

Glycation induces expansion of the molecular packing of collagen.

Exposure of rat tail tendon to a reducing sugar results in covalent attachment of the sugar to collagen, a process termed glycation, and leads to the formation of stable intermolecular cross-links. We have used X-ray diffraction to study the changes in the crystalline unit cell of rat tail tendon collagen brought about by glycation. Ribose was selected as a model compound for most of the study because its reaction with proteins is faster than that of glucose, and therefore more convenient for laboratory studies, but glucose and glyceraldehyde were used as well. A kinetic model describing the process of glycation by ribose and subsequent cross-link formation has been developed. Glycation resulted in an expansion by more than 12% of the unit cell that describes the three-dimensional structure of rat tail tendon collagen. The expansion was in a direction perpendicular to the axes of the rod-shaped molecules, indicating that the intermolecular spacing of the collagen increased. Thus, the structure of collagen in rat tail tendon is significantly altered by glycation in vitro. The expansion was not isotropic, but was directed parallel to the (120) planes, one of the three major planes of the quasi-hexagonal structure that is densely populated by collagen molecules. It is hypothesized that this expansion is brought about by the formation of one, or at most a few, specific intermolecular cross-links in the overlap zone that act to push the molecules apart. It is likely that similar structural changes in collagenous tissues are caused by glycation in vivo during the natural course of aging, and that these changes are accelerated in chronic hyperglycemia such as that associated with diabetes. Analysis of the structure of glycated rat tail tendon potentially can give us new insight into the detailed molecular structure of collagen.

Animals↗
PubMed1986

Structures of D-threo-2,5-hexodiulose 1-phosphate and D-threo-2,5-hexodiulose 1,6-bisphosphate (5-keto-D-fructose mono- and bis-phosphate) in solution by 13C-N.M.R. spectroscopy.

The mono- (2) and bis-phosphate (3) derivatives of D-threo-2,5-hexodiulose (1) (5-keto-D-fructose) were synthesized enzymically and purified by anion-exchange chromatography. The proportions, sizes of ring, and anomeric configurations were determined by F.t. 31P- and 13C-n.m.r. spectroscopy. Compound 2 was found to exist preponderantly (70-78%) in the beta-pyranose form with the remainder existing in the 2R,5R-furanose form. Compound 3 assumes two different furanose forms in solution, one (77-84%) being the 2R,5R-furanose form and the other the 2S,5R-furanose form.

Carbohydrate Conformation↗
PubMed1985

Oxidation rates of some desialylated glycoproteins by galactose oxidase.

Patterns of oxidation of dilute solutions of desialylated fetuin and submaxillary mucin by galactose oxidase have been examined. A significant portion (20-40%) of the terminal galactosyls exposed on the glycoproteins, which theoretically were expected to be accessible to the enzyme, was not oxidized. In comparison, galactosyls in oligosaccharides released from completely desialylated glycoproteins were oxidized more effectively with an apparently lower degree of crypticity to the enzyme. Partial desialylation usually resulted in a reduction of both the rate and the final level of substrate oxidation. A second cycle of oxidation of a desialylated substrate earlier oxidized by galactose oxidase and then reduced by NaB3H4 revealed a selectivity in the pattern of galactosyl oxidation. The same galactosyl residues oxidized in the first cycle were again the most susceptible to oxidation in the second cycle, leaving unmodified the same fraction of galactosyls throughout both cycles. The relevance of these results to the application of the galactose oxidase-NaBH4 procedure for detecting and measuring desialylated glycoconjugates in solution and in biological membranes is discussed.

Animals↗
PubMed1983

A simple spectrophotometric determination of formaldehyde and other aldehydes: application to periodate-oxidized glycol systems.

A simple, rapid, and sensitive spectrophotometric assay procedure for the determination of as low as 2 microM solutions of formaldehyde and acetaldehyde using an alkaline 4-amino-5-hydrazino-3-mercapto-1,2,4-triazole reagent is described. The method is particularly useful for determination of these aldehydes (0.5-50 nmol) when produced by the periodate oxidation of various glycols and can be applied to the assay of dilute solutions of sugars or polyols.

Acetaldehyde↗
PubMed1979

Reduction of nicotinamide adenine dinucleotides by sodium cyanoborohydride.

The relatively slow reduction of NAD+ and NADP+ by sodium cyanoborohydride leads to formation of the enzymically active form of NADH and NADPH. This reaction could be useful as a simple procedure to enzymically introduce a specific label into substrates when tritiated or deuterated cynanoborohydride is used for obtaining the reduced nicotinamide adenine dinucleotide.

Borohydrides↗
PubMed1975

Interactions between aerolysin, erythrocytes, and erythrocyte membranes.

Aerolysin, a hemolytic and lethal exotoxin of Aeromonas hydrophila, was analyzed for amino acids. Assuming 8 histidine residues/mol, the purified toxic protein has, by summation, a molecular weight of 49,000, a value in agreement with earlier estimates by other methods. Erythrocytes from different animal species differ greatly in sensitivity to aerolysin's lytic action. There is some correlation between sensitivity and phosphatidyl choline content. Erythrocyte membranes of different species bind the toxin, and the efficiency of binding is a function of sensitivity to lysis. Binding is temperature independent, is not dependent upon membrane sialic acid, and is decreased by prior treatment with phospholipase C and proteases. Preparations of aerolysin convert substantial amounts of membrane phosphorus to water-soluble form; the conversion is concentration and temperature dependent. Most of the conversion is attributable to contaminating phospholipase(s) that is separable from the toxin. Aerolysin purified by electrophoresis in polyacrylamide gel retains some phospholipase activity, and this activity may or may not be a contaminant.

Aeromonas↗