Collagen made of extended -chains, procollagen, in genetically-defective dermatosparaxic calves.

Abstract

Collagen has been extracted from the skin of dermatosparaxic calves and fractionated by acrylamide-gel electrophoresis and CM-cellulose chromatography. This collagen contains in large proportion two additional types of α-chains, P-α1 and P-α2. The first, P-α1, ressembles α1, of a collagen extracted from the skin of a normal calf in its amino-acid composition but its molecular weight is 10% larger. The second, P-α2, is similar to a normal α2 in its amino-acid composition but its molecular weight is increased by 5%. The abnormal α-chains contain six to eight half cystine residues in p-α1 and one in p-α2. As seen under the electron microscope on segment long spacing, the dermatosparaxic collagen is 25 nm larger than the normal collagen and the in creased length results from extension of the polypeptide chain at the N-terminal extremity of the molecules. Although the collagen is less extractable from the dermatosparaxic skin than from the normal skin and dimers and other polymers of the abnormal α-chains are observed, the dermatosparaxic collagen does not, in vitro, form fibrils of normal stability. Since an enzyme activity which can excise the N-terminal extension peptide of the dermatosparaxic collagen has been identified in extracts of normal skin but is absent in the dermatosparaxic animals, it is suggested that the dermatosparaxic collagen is a form of “procollagen”, from which all or a part of these peptides have not been removed and that such peptides function as coordinators in the post synthesis assembly of the collagen α-chains.