Further hydroxylation of lysyl residues in collagen by protocollagen lysyl hydroxylase in vitro.
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abstract
Additional hydroxylation of lysyl residues in collagen was studied by incubation of several collagens in vitro with partially purified protocollagen lysyl hydroxylase. All collagens tested served as substrates for further hydroxylation if they were thermally denatured before reaction with the enzyme. With large amounts of the enzyme the degree of hydroxylation of lysyl residues in calf skin collagen increased from about 20 to over 40%. In experiments with isolated 1 and 2 chains, additional hydroxylysine was synthesized to a greater extent with al chains than with 2 chains. However, the initial hydroxylysine content in al chains is only about half of that in 2 chains and, therefore, the final hydroxylysine content of the 2 chains was larger than that of the 1. The peptide 1-CB8-HA1 obtained by hydroxylamine cleavage of a specific cyanogen bromide peptide from the 1 chain of rat skin collagen was also tested as a substrate. The 99 amino acids in the peptide were previously sequenced and the level of hydroxylation of the two lysyl residues in the peptide was found to be only about 10%. The peptide served as a substrate for further hydroxylation, but lysyl residues in this peptide were less susceptible to hydroxylation than lysyl residues in whole collagen. The difference may be attributable to the amino acid sequences adjacent to the two lysyl residues in the peptide. In contrast to the results obtained with denatured collagens, the degree of hydroxylation of native collagen was very low, and most or all of the hydroxylation observed with native collagen can be explained by the presence of small amounts of denatured collagen. The results suggest, therefore, that the formation of a triple-helical structure may be one of the critical factors limiting the degree of hydroxylation of lysyl residues during collagen biosynthesis. 1973, American Chemical Society. All rights reserved.
