Denatured Collagen from the Cuticle of Ascaris lumbricoides as a Substrate for Protocollagen Proline Hydroxylase

Abstract

Abstract Recent studies have shown that the hydroxyproline and hydroxylysine found in the collagen of vertebrates are synthesized by the hydroxylation of proline and lysine, which have been incorporated into a large polypeptide precursor of collagen called protocollagen. Because the collagen isolated from the cuticle of Ascaris lumbricoides contains less hydroxyproline and hydroxylysine than any other known collagen, it was of interest to determine whether this collagen could serve as a substrate for the synthesis of hydroxyproline by protocollagen proline hydroxylase from a vertebrate source. Essentially no synthesis of hydroxyproline was observed when the hydroxylase from chick embryos was incubated with native cuticle collagen solubilized by either 0.5 m NaCl extraction or pepsin treatment. Both of these large aggregate forms of the collagen, however, served as substrates for hydroxyproline synthesis after they were denatured by heating at 100° for 10 min. A subunit form of the collagen with a lower specific optical rotation than the large aggregate preparations served as a substrate without prior heat treatment, but the rate of hydroxyproline synthesis was increased by boiling the preparation. Comparison of the relative substrate activities and specific optical rotations of various forms of the cuticle collagen indicated an inverse relationship between the rate of hydroxyproline synthesis and the apparent degree of helicity. Previous reports by others have suggested that the subunit structure of collagen from Ascaris cuticle may involve a helical conformation different from that found in other collagens, and it is possible that an unusual conformation of the polypeptide chain or chains of the native cuticle collagen may explain its inability to serve as a substrate for protocollagen proline hydroxylase.