Hydroxylation of (X-Pro-Gly)n by protocollagen proline hydroxylase Effect of chain length, helical conformation and amino acid sequence in the substrate

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A series of peptides containing sequences of -X-Pro-Gly- were synthesized by a solid-state method which gave homogeneous products. These peptides were then used to study the synthesis of hydroxyproline by protocollagen proline hydroxylase. Hydroxylation of random-coil forms of the series of peptides (Pro Pro-Gly)n with n = 5, 10, 15 and 20 indicated no difference among the peptides in V but the Km decreased markedly with chain-length. Hydroxylation of (Pro-Pro Gly)10 in the triple-helical conformation clearly demonstrated that the triple-helical conformation does not in itself prevent hydroxylation. The V for the helical form was 64% of the V for the random-coil form but the Km in molar concentrations was the same for both forms. Hydroxylation of the peptides Arg-Gly-(Pro-Pro-Gly)5 and Glu-Gly (Pro-Pro Gly)5 indicated that the presence of a basic amino acid in the NH2-terminal end decreases the Km. Comparison of three more complex peptides indicated that modifications of amino acids in the -X-Pro-Gly- triplets which are hydroxylated as well as modified in adjacent triplets can affect the reaction with protocollagen proline hydroxylase.

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