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D J Prockop

Publications and source records attributed to D J Prockop.

At least 415 records · Page 23Linked to original sources
PubMed1967

Intracellular pool of unhydroxylated polypeptide precursors of collagen.

The hydroxyproline and hydroxylysine in collagen are synthesized by an apparently unique pathway in which proline and lysine are hydroxylated after they are incorporated into a large polypeptide precursor of collagen called protocollagen. When the hydroxylation of protocollagen in isolated tissues is intermittently interrupted, hydroxylation can occur after complete polypeptides are released from ribosomal complexes. Cartilage from chick embryos was incubated with the iron chelator alpha,alpha'-dipyridyl for 2 hours to inhibit protocollagen hydroxylase, and then the inhibition was reversed by transferring the tissues to medium containing ferrous iron and no alpha,alpha'-dipyridyl. "Pulse labeling" of the tissues during these two periods indicated that both the accumulated protocollagen and the polypeptides synthesized after reversal of the inhibition were hydroxylated at the same rate. Even when no measures are taken to inhibit the hydroxylation of protocollagen, most of the hydroxyproline in collagen is probably synthesized after complete protocollagen polypeptides are released from ribosomes.

Animals↗
PubMed1967

Partial characterization of protocollagen from embryonic cartilage.

1. Attempts were made to isolate and characterize the protocollagen that accumulates in connective tissue when the hydroxylation of proline and lysine is inhibited. The term protocollagen has been used to describe the proline-rich and lysine-rich polypeptide or polypeptides that serve as substrates for the formation of hydroxyproline and hydroxylysine during the synthesis of collagen. 2. Both protocollagen and newly synthesized collagen from embryonic cartilage were isolated as complex aggregates, which contained sulphated mucopolysaccharides and other proteins or polypeptides from the same tissue. The complexes containing protocollagen were similar to those containing newly synthesized collagen when examined with several different techniques. 3. After the complexes were denatured and disaggregated, zone centrifugation and gel filtration indicated that the denatured protocollagen was similar to the denatured newly synthesized collagen obtained from cartilage in which the hydroxylation was not inhibited, and it was also similar to purified alpha-collagen. The results suggest that, when the hydroxylation is inhibited, most of the protocollagen polypeptides that accumulate are as large as complete alpha-chains of collagen. 4. Significant purification of the protocollagen polypeptides was obtained with a new technique for DEAE-Sephadex chromatography in which urea was used to prevent aggregation of the samples and the column was eluted with guanidine thiocyanate. 5. Protocollagen polypeptides were completely hydrolysed to diffusible peptides by a specific collagenase. 6. It is not entirely clear whether the hydroxylation normally begins while relatively short protocollagen molecules are still attached to polysomes, or whether protocollagen molecules of the size of alpha-collagen are synthesized even when the hydroxylation is not inhibited. 7. Results obtained with puromycin suggest that some hydroxylation occurs with smaller polypeptides, but polypeptide chains approaching the size of alpha-collagen are required to obtain complete hydroxylation of the appropriate amino acid residues of protocollagen.

Animals↗
PubMed1967

Collagen degradation and the response to parathyroid extract in the intact rhesus monkey.

Proline-(14)C was administered to five adult rhesus monkeys, and the degradation of collagen was followed by the excretion of hydroxyproline-(14)C. The results suggested the presence of at least three separate pools of collagen with half-lives of 1 to 2, 2 to 3, and 50 to 70 days. The monkeys were killed after 44 days; at that time the specific activity of the hydroxyproline-(14)C in urine was found to be four to five times that of the hydroxyproline in soluble collagen and 81 to 93% that of hydroxyproline in insoluble collagen. The relationships between urinary hydroxyproline and the degradation of collagen were similar to those previously demonstrated in rats. Parathyroid hormone was administered daily to two of the monkeys from the 27th to the 44th day of the study. The parathyroid hormone increased the amount of hydroxyproline-(14)C excreted, but there was no significant change in the specific activity of the urinary hydroxyproline-(14)C. Since under the conditions of the experiment insoluble collagen was the only possible source of hydroxyproline-(14)C of relatively high specific activity, the results indicated that parathyroid hormone directly or indirectly increased the degradation of insoluble collagen. The results also suggested that parathyroid hormone increased the degradation of soluble collagen, but the relative magnitude of this effect was not clearly established.

Animals↗
PubMed1966

Hydroxylation of proline and the intracellular accumulation of a polypeptide precursor of collagen.

Autoradiographs of embryonic cartilage indicated that labeled protein accumnulated intracellularly when the tissue was incubated with tritiated proline, and when the hydroxylation of proline was inhibited by anaerobic conditions or by a chelator for ferrous iron. The labeled protein apparently corresponds to protocollagen. the polypeptide precursor of collagen which serves as a substrate for the enzymatic synthesis of hydroxyproline.

Animals↗