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Biomedical subjects

A Veis

Publications and source records attributed to A Veis.

At least 127 records · Page 7Linked to original sources
PubMed1978

The visualization of individual collagen molecules and aggregates in collagen solution: the effect of preparation and sampling techniques.

The use of electron microscopic observations to characterize the state of aggregation of collagen molecules in solution has been examined from the point of view that the observed structures must be compatible with the physical chemical properties of the solution. The common procedure of addition of droplets of a collagen solution to a grid followed by negative staining produces aggregates on the grid which could not have represented the aggregation state in solution. Closer representation of fibril diameters can be achieved by freeze cleave-etch methods. The best representation of the state of aggregation in collagen solutions can be achieved by use of a careful drop-washing procedure. This procedure, described in detail, permits correlation between intrinsic viscosity and electron microscopic observations.

Collagen↗
PubMed1977

Biochemical identification of homogentisic acid pigment in an ochronotic egyptian mummy.

Roentgenograms of an Egyptian mummy, dating from 1500 B.C., showed extensive calcification of the intervertebral discs and articular narrowing in both hip and knee joints. Biopsy cores from the right hip showed parallel black zones in the region of the articular surfaces, leading to a clinical diagnosis of ochrinosis. The black pigment was extracted, analyzed, and compared to an air-oxidized homogentistic acid polymer. The two substances apparently were identical. The chemical evidence thus confirms the clinical finding of ochronosis, an autosomal recessive disorder. This is, so far as known, the earliest verified case of this disorder.

Cartilage↗
PubMed1977

The solubilization of bone and dentin collagens by pepsin. Effect of cross-linkages and non-collagen components.

Bone and dentin collagen are less susceptible to solubilization by pepsin digestion then is skin collagen. Digestion at 4 degrees C for 72 h solubilized only 35.3% of bovine cortical bone and 5.6% of bovine dentin compared with nearly 100% dissolution of bovine skin. Sodium dodecyl sulfate-acrylamide gel electrophoresis and molecular sieve chromatography showed that, for bone and dentin, intact alpha chains and cross-linked aggregates of beta, gamma and higher weight remained intact after pepsin solubilization but lower molecular weight fragments also were prevalent indicating chain scission in helical regions. Electron microscopic examination of segment long spacing precipitates of the soluble collagens confirmed the presence of solubilized polymerized collagen. The principal reducible cross-link in both bone and dentin was the precursor of dihydroxylsinonorleucine and this cross-link was also present in the solubilized collagens. Small amounts of non-collagenous proteins and glycosaminoglycans of different compositions in dentin and bone resisted extraction before pepsin digestion. However, the differences in solubilization of the collagens have been related to differences in cross-linkage placement.

Amino Acids↗
PubMed1977

Triple-helix formation on ribosome-bound nascent chains of procollagen: deuterium-hydrogen exchange studies.

Polyribosomes containing nascent [3H]proline-labeled collagen chains were isolated from chick embryo fibroblasts in culture. These nascent chains were nearly completely hydroxylated, as indicated by the presence of [3H]hydroxyproline and high hydroxyproline/proline ratios. The polyribosomes were suspended in D2O at 15 degrees and the infrared spectrum was determined using a reference cell containing collagen-depleted polyribosomes in D2O, matched to equal RNA content. The amide I and amide II bands were observed. When the polyribosomes were heated in D2O at 44 degrees in the infrared cells, the N--D amide II absorbance at 1480 cm-1 increased markedly, indicating that H leads to D exchange had occurred. Collagen-depleted polyribosomes showed no such changes in absorbance at 1450-1480 cm-1 upon heating. Polyribosomes recovered from the infrared cells after treatment at 44 degrees and cooling still contained collagen, as indicated by their [3H]hydroxyproline content. These data indicate that nascent collagen bound to the polyribosomes can assume a hydrogen-bonded structure. Taken with prior data showing that the nascent collagen was also resistant to pepsin digestion, it is suggested that the collagen examined is in triple-helix conformation. Because the nascent polyribosome-bound collagen is nearly fully hydroxylated, it must be considered that triple-helix formation can occur between nascent chains while they are attached to the endoplasmic reticulum surface and that chain association and triple-helix formation in vivo may well occur before rather than after release.

Animals↗
PubMed1976

Intracellular location of triple helix formation of collagen. Enzyme probe studies.

Primary cultures of chick embryo fibroblasts were used to study ribosomal events in the processing of procollagen. Polyribosomes from radiolabeled cells were subjected to enzyme probe analysis using collagenase and pepsin digestion to assess both the amount of procollagen present on the polyribosomes and the conformation of the molecule. The peptides rendered dialyzable by each enzyme treatment were analyzed for radioactive proline and hydroxyproline. Approximately 30% of the nascent proteins were collagenous. Although some hydroxyproline was dialyzable in the pepsin-treated material, a low ratio of hydroxyproline to proline (0.04) indicated that considerable amounts of noncollagenous proteins were digested. Polyribosomal material, previously treated with pepsin, was digested with purified collagenase. Similarly, collagenase-digested polyribosomes were treated with pepsin. The pepsin pretreatment released noncollagenous protein and served to purify the remaining ribosomally bound pepsin-resistant collagenous protein. Collagenase treatment of the pepsin-resistant ribosomally bound peptides released peptides with a hydroxyproline to proline ratio of 0.65, indicating that considerable hydroxylation of proline occurs on nascent ribosomally bound procollagen. This finding combined with the well documented stabilizing effect of hydroxyproline on the collagen triple helix and the demonstrated resistance of ribosomally bound procollagen to pepsin digestion indicates that the collagen triple helix may well form on the polyribosome.

Animals↗
PubMed1976

The identity of a cyanogen bromide fragment of bovine dentin collagen containing the site of an intermolecular cross-link.

A peptide fraction isolated from a cyanogen bromide digest of bovine dentin collagen had a molecular weight of 46000. Its size and amino acid composition indicated that it could not consist of peptides derived from the cleavage of a single alpha chain. On reduction with tritiated sodium borohydride, radioactivity was incorporated primarily into 5, 5'-dihydroxylysinonorleucine without degradation at the peptide backbone. Periodate cleavage of the reduced or nonreduced peptide fraction generated one fragment of molecular weight 28000 and one of 18000 completely accounting for the size of the parent peptide. On amino acid analysis the constituent single-chain peptides were determined to be alpha2CB4 and alpha1CB6. Both peptides isolated after periodate oxidation of the tritiated borohydride reduced cross-link peptide were found to contain (3H)hydroxynorvaline. These data show that some hydroxylysine of alpha2CB4, a helical region peptide, was present in aldehyde form and could act as the aldehyde donor icross-link, Schiff's base formation. The only cross-linkage of this alpha2CB4 acting as an aldehyde donor peptide to alpha1CB6 would be a helical region to helical region bond, perhaps accounting for the unusual stability and low solubility of dentin collagen.

Amino Acids↗
PubMed1976

The cyanogen bromide peptides of bovine soluble and insoluble collagens. I. Characterization of peptides from soluble type I collagen by sodium dodecylsulphate polyacrylamide gel electrophoresis.

Acid soluble collagen and purified alpha1 and alpha2 chains were prepared from bovine skin and digested with cyanogen bromide. The resultant peptides were separated by electrophoresis on polyacrylamide gels containing sodium dodecylsulphate. Thirteen peptides obtained from the alpha1 chain and two from the alpha2 chain were identified as overlapping sequences containing methionine-derived peptide bonds not cleaved during the reaction. Those uncleaved peptides from the alpha1 chain accounted for approximately 30% of the total digest, as determined by planimetry on the staining profiles, and their relative proportions indicated that efficiency of cleavage at specific methionine residues was dependent upon position in the sequence. Alpha1CB5-8 was most resistant to cleavage while alpha1CB0,1-2 and alpha1CB7-6 were most susceptible. Peptides of a 2:1 (w/w) mixture of alpha1 and alpha2 chains and of the acid-soluble collagen gave electrophoretograms which were essentially a summation of those obtained from the individual chains.

Animals↗
PubMed1976

The cyanogen bromide peptides of bovine soluble and insoluble collagens. II. Tissue specific cross-linked peptides of insoluble skin and dentin collagen.

Cyanogen bromide peptides were prepared from insoluble bovine skin and dentin collagens and compared by electrophoresis in polyacrylamide gels containing sodium dodecylsulphate, with those of the alpha1 and alpha2 chains of soluble type I and type III collagen. Both insoluble collagens yielded predominantly the peptides of type I collagen. Insoluble skin collagen was approximately 13% type III. Type III collagen if present in dentin, is present in smaller quanitity not detected by the technique used here. Several new fragments, different in each tissue, were obtained which could not be accounted for as uncleaved peptides. Three of those from dentin were isolated by gel chromatography and characterized by amino acid analysis. Two were found to contain 3-hydroxyproline, suggesting the presence of alpha1CB6. The recovery of only 25-30% of alpha1CB6 in the expected position on SDS gel electrophoresis indicated that it was involved in interactions with other peptides in these two tissues to the extent of one and a half cross-links per tropocollagen molecule. The nature and distributin of cross-link peptides of bovine skin and dentin collagens was distinctly different.

Amino Acids↗
PubMed1975

The extraction of phosphoproteins from bovine dentin.

The phosphoprotein obtained by the neutral pH tris buffer extraction of acetic acid demineralized bovine dentin has been compared with the phosphoprotein extracted directly during the neutral pH EDTA demineralization process. The phosphoproteins isolated by DEAE-cellulose chromatography from the neutral pH EDTA demineralization extract are not identical to those isolated by the same procedure from the dentin which had been subjected to acid demineralization. The two demineralization procedures yield phosphoproteins different in amino acid content and in presence of 260 nm UV absorbing moiety. Even after sequential acid demineralization, trisbuffer extraction and EDTA extraction, the residual dentin contains phosphoprotein. A peptide fragment containing both collagen and phosphoprotein moieties has been isolated following digestion and cleavage of the insoluble dentin collagen with cyanogen bromide. The acid demineralization process appears to be accompanied by degradation which removes both protein and non-protein components from the phosphoprotein.

Acetates↗
PubMed1975

Evidence for abnormality of bone-matrix proteins in osteogenesis imperfecta.

Immunological and biochemical techniques demonstrated that the non-collagenous proteins of the organic matrix of bone were abnormal in quantity and composition in four children with osteogenesis imperfecta. This represents the main molecular difference found so far between bone in osteogenesis imperfecta and normal bone.

Adolescent↗