Type V collagen from the chick embryo: biochemical, physicochemical and ultrastructural characteristics.

Two collagen alpha chains have been isolated from whole 17 day chick embryos which are similar to the B chain or alpha 1(V) and the A chain or alpha 2(V) recently described in mammalian and avian tissues. A non-collagenous acidic protein was co-purified with the Type V collagen which was resistant to pepsin digestion. The molecular weight, circular dichroism spectrum, melting temperature and diffusion coefficient of the native Type V collagen and isolated alpha chains were similar to values obtained for other chick collagen types. The SLS crystallite of Type V collagen had a distinct pattern of banding as identified by electron microscopy. We consistently observed more alpha 2(V) than alpha 1(V) following both CM-cellulose and QAE-Sephadex ion exchange chromatography of denatured Type V collagen, but unusual solubility properties and recoveries of the alpha 1(V) chain may have diminished its relative amount. In addition we have found that the alpha 1(V) chains are chemically heterogeneous and one component electrophoreses as an alpha 2(V) chain on SDS gels.

Nonenzymatic hydroxylations of proline and lysine by reduced oxygen derivatives.

The biosynthesis of trans-3- and trans-4-hydroxyprolines and 5-hydroxylysine in animal cells requires polypeptide proline or lysine, enzymes and cofactors including iron, and possibly involves peroxidatic intermediates. Several laboratories have reported the presence of low-molecular-weight hydroxyproline and hydroxylysine peptides in cell and organ cultures. We found that these small peptides contained the trans-3 and cis-4 isomers of hydroxyproline as well as trans-4 ones and that their production was not completely inhibited by alpha, alpha-dipyridyl, and iron chelator and effective inhibitor of enzyme-mediated hydroxylations. It is known that oxygen or hydrogen peroxide in the presence of metal can hydroxylate proline and other aromatic compounds. We show here that reduced oxygen derivatives can hydroxylate both free and polypeptide-bound proline and lysine, and that scavengers of hydroxyl radicals suppress, but do not completely inhibit, this reaction. Reduced oxygen derivatives can be generated in normal and pathological circumstances, and some of the low-molecular-weight hydroxyproline and hydroxylysine peptides found in cell and organ cultures might be derived from these derivatives and therefore do not reflect collagen turnover, but rather some other cellular activity.