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Biomedical subjects

J A Foster

Publications and source records attributed to J A Foster.

At least 127 records · Page 7Linked to original sources
PubMed1980

Comparison of aortic and ear cartilage tropoelastins isolated from lathyritic pigs.

Tropoelastin was isolated from aortae and auricular cartilage obtained from lathyritic piglets. The two tissue-specific tropoelastins were judged homogeneous by sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel filtration on a high-pressure liquid chromatograph. Comparative studies of the tropoelastins were performed. Amino acid analysis revealed that the aortic and cartilage tropoelastins were very similar, if not identical, with the only exception that the cartilage tropoelastin contained more hydroxyproline and less lysine residues, both of which can be attributable to post-translational modifications. Both tropoelastins possess an apparent molecular weight of 70 000 and exhibit similar peptide fragments with limited trypsin cleavage. Antiserum raised to the aortic tropoelastin was used to show immunological identity between the two tissue tropoelastins.

Amino Acid Sequence↗
PubMed1980

Translation of chick aortic elastin messenger ribonucleic acid. Comparison to elastin synthesis in chick aorta organ culture.

Studies were undertaken to define the molecular size of the elastin primary gene product. Translation of chick aortic messenger ribonucleic acid (mRNA) in an mRNA-dependent reticulocyte lysate resulted in the synthesis of two major proteins of 70 000 and 73 000 molecular weights. Both proteins were shown to be soluble forms of elastin by isotope incorporation, immunoprecipitation, collagenase and cyanogen bromide sensitivity, and two-dimensional gel electrophoresis. The 70 000-dalton protein behaves similarly to authentic tropoeleastin in sodium dodecyl sulfate gel electrophoresis. There was no evidence for a high molecular weight form of soluble elastin, although procollagen chains were indirectly identified among the aortic mRNA-directed translation products. The same molecular size proteins were also seen in organ cultures of chick embryonic aortas labeled with [3H]valine. However, the 73 000-dalton protein was not extractable in a neutral salt buffer but was found only if the aortas were extracted with urea in the presence of reducing and alkylating reagents. The results from these studies suggest that elastin is first synthesized as two distinct polypeptide chains which differ slightly in size and overall charge. The possibility that these two proteins may associate posttranslationally to form a dimer prior to secretion is postulated to explain the existence of a putative proelastin molecule seen in other systems.

Animals↗
PubMed1980

Intracortical origin of recruiting responses in the cat cortex.

Field potentials associated with recruiting responses produced by low-frequency stimulation of non-specific thalamic sites were simultaneously recorded from an intracortical tri-probe and the pial surface. Separation of the tri-probe tips along the probe axis (typically 100 mum) permitted discrimination of spatial field potentials. Analyses were performed on the data to provide estimates of the intracortical locations of the ion sources and sinks giving rise to the surface negative recruiting response. At the peak of a recruiting response event, the results suggest a sink in Brodmann layer II simultaneous with a source in layers III, IV and V. A hypothesis of a simultaneous 'push-pull' spatial modulation of pyramidal cell activity in layer II with the activity of pyramidal cells in layers IV, V and VI is proposed.

Animals↗
PubMed1979

The anti-proteolytic behavior of lathyrogens.

The lathyrogens, beta-aminopropionitrile and alpha-aminoacetonitrile inhibit both the esterolytic and proteolytic activity of trypsin at a concentration of 100 mM. Lineweaver-Burk plots demonstrate that inhibition is competitive, with alpha-aminoacetonitrile being the more potent inhibitor. The enzyme associated with and capable of digesting tropoelastin is inhibited by both lathyrogens when tested against its natural substrate, tropoelastin. Administration of alpha-aminoacetonitrile-HCl to the diet of young chicks (0.1% w/w) resulted in a 62% increase in the yield of tropoelastin and significant reduction in fatality as compared to beta-aminopropionitrile-fumarate.

Acetonitriles↗
PubMed1979

Characterization of insoluble elastin from copper-deficient pigs. Its usefulness in elastin sequence studies.

Insoluble elastin from copper-deficient animals has an amino acid composition intermediate between mature elastin and salt-soluble elastin (a higher lysine content and correspondingly low number of cross-links relative to the normal protein) and is solubilized by successive treatment with trypsin and chymotrypsin at 4 and 37 degrees C. Small amounts of B3H4 (11 mg--2 g of elastin) reduced allysine, allysine aldol, dehydronorleucine, and dehydromerodesmosine in insoluble elastin from copper-deficient pig aorta. In contrast, desmosine and isodesmosine were reduced only when a large excess of reductant (400 mg borohydride) was included in the reaction mixture. Reduction studies indicated that lysinonorleucine and merodesmosine were present in their dehydro forms to a greater extent in copper-deficient pig elastin than in normal elastin. After reduction with borohydride approximately 35% of the reduced form of the insoluble elastin remained insoluble after digestion with trypsin and chymotrypsin. A peptide containing the aldehyde oxidation product of lysine (allysine) and demonstrating an enrichment in glutamic acid was purified from the reduced form of copper-deficient pig elastin and partially sequenced. Its sequence (Gly-Ala-Glu-allysine-(Glu)...) and amino acid composition suggest: (1) clustering of glutamic acid residues in the elastin molecule, and (2) that allysine residues are not restricted to the alanine-enriched sites described for other elastin cross-links. Insoluble elastin from copper-deficient animals promises to be a useful tool for elastin sequence studies.

Amino Acid Sequence↗
PubMed1978

A structural model for desmosine cross-linked peptides.

Desmosine-enriched peptides were isolated from a thermolysin digest of bovine ligamentum nuchae elastin and a partial sequence was determined. A 'two-cross-link' model is proposed in which a second cross-link, perhaps lysinonorleucine, joins two peptide chains approx. 35 amino acid residues removed from the desmosine. Implied in this model is a certain asymmetry or directionality which places restrictions on the 'sense' of the peptide chains (either always parallel or anti-parallel) in order to align the cross-linking sites. Imposing such restrictions raises the possibility of specific alignment of elastin precursor molecules by microfibrillar proteins and/or aligning peptides on the precursor molecules themselves.

Amino Acid Sequence↗
PubMed1977

Trypsin-like neutral protease associated with soluble elastin.

Isolation of tropoelastin is complicated by the presence of a neutral protease closely associated with tropoelastin that is capable of sequentially degrading tropoelastin to small peptides. Substrate and inhibitor specificities of this neutral protease associated with purified tropoelastin were examined. The enzyme displayed proteolytic activity against casein, and esterase activity was detected when assayed against N-tosyl-L-arginine methyl ester but not against tert-butyl-oxycarbonyl-L-alanine p-nitrophenyl ester. No appreciable elastinolytic activity was detectable against either insoluble sodium dodecyl sulfate treated elastin or maleylated tropoelastin. The enzyme was not inhibited by the chymotrypsin inhibitor toluenesulfonylphenylalanine chloromethyl ketone. The enzyme was inhibited by phenylmethanesulfonyl fluoride and, to various degrees, by metal chelators. Tosyllysyl chloromethyl ketone, epsilon-aminocaproic acid, and Aprotinin (pancreatic trypsin inhibitor--Kunitz type), all inhibitors of trypsin-like enzymes, were very effective inhibitors, as were soybean trypsin inhibitor and human alpha-1-antitrypsin. The data suggest that the tropoelastin-associated enzyme is a neutral serine protease with trypsin-like specificity.

Amino Acids↗
PubMed1977

Proteolysis of tropoelastin.

The presence of an enzyme associated with tropoelastin is described. The enzyme has a pH optimum between 7 and 9 and trypsin-like specificity. Upon incubation, tropoelastin (72,000 molecular weight) is cleaved into relatively high molecular weight fragments. In addition to the parent molecule, five discrete polypeptide bands are usually observed on SDS gels with molecular weights of approximately 57,000, 45,000, 36,000, 25,000 and 13-14,000.

Aminopropionitrile↗
PubMed1977

Role of crosslinking in fiber formation.

The synthesis of elastin by smooth muscle cells is demostrated by amino acid analyses and the presence of lysine-derived crosslinks. The data reveal that the ratio of allysine to aldol decreases with time in culture. The presence of insoluble elastin correlates well with the presence of the reduced aldol condensate in these cells. If the formation of the desmosines occurs by the condensation of the aldol and dehyrolysinonorleucine, the presence of the latter may be rate-limiting since the cells display little or no dehydrolysinonorleucine. Several peptides containing the desmosine crosslink were purified and partially sequenced. The data indicate that desmosines crosslink two polypeptide chains and that both desmosine and isodesmosine are present in the same primary sequence approximately equally substituted. A possible role for tyrosine in the regulation of desmosine formation is presented.

Aldehydes↗
PubMed1976

Intrinsic enzyme activity associated with tropoelastin.

The presence of an enzyme(s) associated with purified tropoelastin has been established. Results indicate that the enzyme(s) remains closely associated with the soluble elastin throughout the entire purification procedure suggesting that it is very tightly bound. Enzymatic activity is optimum through the pH range 7-9 (37 degrees C) and can be inhibited by disodium ethylenediaminetetraacetate, N-ethylmaleimide, sulfite, soybean trypsin inhibitor and human alpha-1-antitrypsin. The fragmentation pattern appears to be specific and reproducible.

Amino Acids↗