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N A Kefalides

Publications and source records attributed to N A Kefalides.

At least 91 records · Page 5Linked to original sources
PubMed1976

Carbohydrate moieties of procollagen: incorporation of isotopically labeled mannose and glucosamine into propeptides of procollagen secreted by matrix-free chick embryo tendon cells.

Cells obtained from chick embryo tendons incorporate isotopically labeled glucosamine and mannose into the pro-alpha1 and pro-alpha2 chains of procollagen as judged by sodium dodecyl sulfate-gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The label was further localized to the propeptides of pro-alpha1 and pro-alpha2 by its chromatographic behavior after digestion with bacterial collagenase or alpha-chymotrypsin. Carbohydrate analysis of isolated pro-alpha chains showed the presence of labeled galactosamine in addition to mannose and glucosamine. Resistance to mild alkaline hydrolysis suggested that greater than 90% of the oligosaccharide units are not linked to the propeptide backbone by either serine or threonine.

Animals↗
PubMed1976

Characterization of the collagen synthesized by endothelial cells in culture.

[14C]Proline and [14C]lysine were incorporated into collagen by cultures of endothelial cells derived from calf aortae. The isomer 3-hydroxy[14C]proline accounted for 10% of the total hydroxy[14C]proline in the collagen isolated from the medium. Approximately 81% of the hydroxy[14C]lysine isolated from the medium was glycosylated, and 91% of the glycosylated hydroxy[14C]lysine was in the form of the disaccharide glucosylgalactose. Gel filtration chromatography or acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate indicated that the initially synthesized peptide chain of [14C]collagen had a molecular weight of about 135,000; after pepsin digestion this was converted to 115,000. The ratio of hydroxy[14C]proline to total [14C]proline x 100 in the pesin-resistant fraction was 59. When examined by immunofluorescence microscopy, the endothelial cultures stained positively with antiserum to (Type IV) collagen from basement membrane of bovine anterior lens capsule. The data indicate that cultured endothelial cells derived from calf aortae synthesize collagen that resembles that of basement membrane collagen.

Aorta↗
PubMed1976

Rat parietal yolk sac basement membrane. An investigation of the antigenic determinants using a radioimmunoassay.

Previous studies have shown that there is microscopic and biochemical evidence that rat parietal yolk sac synthesizes basement membrane (type IV) collagen; this study shows that a radioimmunoassay may be used for the detection of type IV collagen in such biosynthetic systems. Rat parietal yolk sacs incubated in medium containing (14C) proline either with or without alphaalpha-dipyridyl produced either unhydroxylated or hydroxylated (14C)collagen. The immunological reactivity of these two preparations was investigated using antibodies to bovine type IV collagen in a radioimmunoassay which demonstrated that the hydroxylated (14C)collagen preparation had a considerably higher level of antigenicity than the unhydroxylated (14C)collagen. Hydroxylated rat type IV (14C)collagen which had been reduced and alkylated was intermediate in antigenicity between hydroxylated and unhydroxylated material. These findings suggest that there are antigenic determinants which depend upon hydroxylation of the collagen molecule, and others dependent upon intact disulphide bonds. In addition, various levels of pepsin extracted unlabelled calf anterior lens capsule collagen caused inhibition of antibody binding to (14C)collagen. Rat type IV (14C)collagen which had been digested with collagenase was inactive in the radioimmunoassay, while pepsin digestion caused no reduction in antigenicity. These findings suggest that the antiserum is directed towards the collagenous part of the molecule and may be a useful tool in the detection of biosynthesized basement membrane collagen.

Alkylation↗
PubMed1976

The role of hydroxylation of proline in the antigenicity of basement membrane collagen.

Rabbit antibodies to bovine basement membrane collagen were used to compare the antigenic determinants of rat parietal yolk sac basement membrane [14C]procollagen with [14C]protocollagen. Basement membrane [14C]protocollagen was found to be less antigenic than basement membrane [14C]procollagen. Hydroxylation of basement membrane [14C]protocollagen, either intracellularly or in vitro with protocollagen prolyl hydroxylase, resulted in restoration of antigenicity. The difference in antigenicity observed between basement membrane [14C]procollagen and basement membrane [14C]protocollagen appeared to depend primarily upon the presence of hydroxyproline in the collagen molecule. Glucosylgalactosylhydroxylysine was found to be unimportant for antigenicity.

Animals↗
PubMed1976

The use of the radioimmunoassay in the characterization of antibodies to basement membrane collagen.

This study describes the use of the radioimmunoassay for the characterization of antibodies to basement membrane (type IV) collagen from bovine anterior lens capsule. The immunogen was extracted from calf anterior lens capsules by limited pepsin digestion and injected into rabbits. The antisera were characterized using gel diffusion, haemagglutination and the radioimmunoassay in which 125I-labelled types I, II, III, and IV bovine collagen were employed. In the direct radioimmunoassay there was no reaction with either native or denatured types I, II or III bovine collagen, whereas there were high titres towards both native and denatured type IV bovine collagen. Radioimmune inhibition studies using unlabelled types I, II, III and IV bovine collagen, collagenase digested and repepsinized type IV collagen showed that there was marked inhibition by either native, denatured or repepsinized type IV collagen, and slight inhibition by native type I collagen; native type II and type III, denatured types I, II and III, and collagenase digested type IV collagen had no inhibitory effects.

Amino Acids↗
PubMed1975

The embryonic rat parietal yolk sac. The role of the parietal endoderm in the biosynthesis of basement membrane collagen and glycoprotein in vitro.

Basement membrane biosynthesis in vitro was studied in a rapidly growing embryonic tissue, the rat parietal yolk sac. This tissue consists of a thick, nonvascular basement membrane (Reichert's membrane) separating two cellular layers (parietal endoderm and trophoblast). Morphologically, Reichert's membrane appeared similar to other basement membranes. Previous analysis of the amino acid and carbohydrate composition of acellular Reichert's membrane showed it to be typical of basement membranes isolated from other tissues and species. Analysis of [14-C]proline incorporation and hydroxy [14-C]proline synthesis during the third quarter ogestation in vitro showed that basement membrane collagen synthesis in the parietal yolk sac was maximal around the 14th day of gestation. At this time, basement membrane collagen represented nearly 10% of the newly synthesized protein. The collagen synthesized in this system was characteristic of basement membrane collagen in that about 11% of the total hydroxy [14-C]proline was present as the 3-isomer. In addition, after incubation in the presence of [14-C]lysine, 83 to 94% of the hydroxy[14-C]lysine was glycosylated, with the predominant form being glucosylgalactosylhydroxy[14-C]lysine. When the parietal endoderm and trophoblast were incubated separately with [14-C]proline, it was determined that the former was solely responsible for the synthesis of basement membrane collagen since essentially all of the 4-hydroxy[14-C]proline was associated with this cell type. Autoradiographic experiments with [3-H]glucosamine also served to localize the synthesis of noncollagen basement membrane glycoprotein components to the parietal endoderm. As with the results reported for basement membrane collagen secretion in embryonic chick lens cells, there appeared to be approximately a 60-min delay between the incorporation of [14-C]proline into protein and the secretion of collagen as measured by the appearance of 4-hydroxy[14-C]proline in the culture medium. Experiments utilizing [3H]glucosamine to monitor glycoprotein synthesis did not show a delay between the incorporation of [3H]glucosamine and the secretion of nondialyzable 3-H into the medium. The results obtained using the parietal yolk sac system to study basement membrane biosynthesis were compared to those previously obtained using the kidney glomerular and embryonic chick lens systems. It was concluded that the parietal yolk sac system is superior for a number of reasons: (a) the extracellular matrix appeared to contain only basement membrane components; there was no contamination by acid mucopolysaccharides or other types of collagen; (b) only a single cell type appeared to be responsible for the synthesis of basement membrane components; and (c) a relatively large percentage of the newly synthesized protein was basement membrane collagen.

Animals↗
PubMed1975

Basement membranes: structural and biosynthetic considerations.

Basement membranes are extracellular matrices synthesized by a variety of cells including the basal cells of the epidermis; the respiratory, gastrointestinal, and glandular epithelium; the capillary endothelium; the epithelial cells of the glomerulus, the renal tubule, and the lens capsule; and the endothelium of Descemet's membrane. Basement membranes in the mature animal are free of lipids, DNA, and proteoglycans and are composed of dissimilar protein subunits. One of these is a procollagen-like molecule associated with a noncollagenous matrix glycoprotein. The proportion of the latter component varies among basement membranes. These various subunits are stabilized by hydrogen bonds, disulfide bonds, and aldehyde-derived cross-links which are so extensive that they render the basement membranes highly insoluble. Immunochemical studies indicate three distinct antigenic components which correspond to the collagenous moiety, its nonhelical extension, and the matrix glycoprotein. The collagen component of basement membranes, free of the nonhelical extension, is composed of three identical alpha-chains. It is highly rich in hydroxylysine, 3- and 4-hydroxyproline and contains 4 to 8 residues of half-cystine. It contains 38 residues of glucosyl-galactosyl-hydroxylysine per chain and minimal amounts of mannose, glucosamine, and fucose. Newly synthesized basement membrane collagen is secreted in the extracellular space as the precursor molecule "procollagen." This molecule does not undergo conversion to collagen but interacts with the matrix glycoprotein to give rise to the appropriate structure.

Amino Acids↗
PubMed1975

Basement membranes: current concepts of structure and synthesis.

Basement membranes are composed of dissimilar protein subunits. The procollagen-like subunit is associated with noncollagenous matrix glycoproteins. The proportion of the latter components varies among basement membranes. The various subunits interact via hydrogen bonds, disulfide bonds and aldehyde-derived cross-links. The extensive degree of cross-linking renders basement membranes highly insoluble. A procollagen-like molecule, extracted from calf anterior lens capsule, exhibits on electron microscopy a filamentous component with a globular portion attached at one end. Treatment of basement membranes with pepsin at low temperature digests the noncollagenous glycoprotein components and allows the collagenous component to come into solution. Purification of the pepsin-solubilized collagen from basement membranes reveals a molecule composed of three identical alpha-chains. Other unique features include 40-50 residues of hydroxylysine, 128-140 residues of 4-hydroxyproline, 12-15 residues of 3-hydroxyproline, 29 residues of arginine, 35 residues alanine, 2-4 residues of half-cystine, 38 residues of glucosyl-galactosyl-hydroxylysine, 3 residues of mannose, 2 residues of glucosamine, and 0.3 residues of fucose. Immunochemical studies indicate the presence of three distinct antigenic components and support the evidence that one is collagenous and the other two are noncollagenous glycoproteins. One of the latter corresponds to the non-helical extension of procollagen. The other is a large-molecular weight highly cross-linked matrix protein.

Amino Acids↗
PubMed1975

Effects of a molecular change in collagen on lung structure and mechanical function.

Semicarbazide, a lathyrogen, was given to growing rats to elucidate the consequences of altering the molecular structure of fibrous proteins within the lung. Static pressure-volume (P-V) measurements during deflation of saline-filled lungs showed normal recoil pressure and compliance values within the physiological range of lung volume. Quasi-static P-V measurements were also normal during slow reinflation, even beyond physiological limits to a recoil pressure of 20 cm H20. However, the lungs of experimental rats ruptured at much lower recoil pressures than controls. Histology was normal in lungs fixed at 20 cm H20. In contrast, lungs showed dilation of terminal air spaces, rupture of alveolar walls, and an increase in mean linear intercept in experimental compared with control specimens, when fixed at 30 cm H20. Biochemical analyses revealed reduced cross-linking of lung collagen without change in its total content. There were no detectable changes in the quantity or quality of lung elastin. It is concluded that semicarbazide may selectively impair the maturation of lung collagen and that immaturity of lung collagen is associated with a reduction in the tensile strength of lung tissue, without changes in elasticity within physiological volume limits.

Animals↗
PubMed1974

Biochemical properties of human glomerular basement membrane in normal and diabetic kidneys.

To determine the presence of any significant structural abnormalities in the glomerular basement membrane (GBM) of diabetic individuals, GBM from normal and diabetic human kidneys were isolated and analyzed chemically and structurally. The amino acid composition of the normal GBM revealed the presence of significant amounts of hydroxyproline, hydroxylysine, glycine, and carbohydrate suggesting the presence of a collagen-like protein. There was no significant increase in the amount of hydroxylysine, hydroxyproline, or in the hydroxylysine-linked glycoside glucosyl-galactose in the diabetic kidneys. There was, however, a significant decrease in the cystine and sialic acid content of GBM from diabetic kidneys. It was further shown that the alpha-chains isolated from the collagens of normal and diabetic basement membranes had similar amino acid and carbohydrate compositions. The hydroxylysine, hydroxyproline, glycine, and hexose contents were higher by 82, 56, 74, and 94%, respectively in the alpha-chains compared with the intact basement membranes from both the normal and diabetic kidneys. The results indicate that the slight increases in hydroxylysine and hexose content observed occasionally in diabetic GBM preparations are of no statistical significance and cannot be attributed to increases in the activities of enzymes which hydroxylate lysine or glycosylate hydroxylysine, respectively.

Adult↗