Type III procollagen and collagen in skin

Abstract

A form of collagen, containing three α chains of type III, can be extracted from foetal calf, calf and rat skin under physiological conditions. This native collagen was purified by DEAE-cellulose chromatography and then was analysed by polyacrylamide gel electrophoresis which showed it consisted of several high molecular weight components, the size of γ components and larger species. Prior reduction in dithiothreitol dissociated these large polymers into two components: the minor one migrated between the α 1(I) and α 2 chains while the predominant one migrated between the α and β chains. These two monomers were isolated by CM-cellulose chromatography. The minor one, which eluted between the α 1 and α 2 chains, had a molecular weight of approx. 95 000; its amino acid composition was similar to that of α 1(III). The major one eluted in the α 1 region and had a molecular weight of approx. 120 000; its amino acid composition, while similar to that of the α 1(III) chain, differed in detail, and it is presumed to be a pro-α 1(III) chain. Following pepsin digestion, the native collagen remained as a disulfide-bonded trimer which dissociated into only one component, α 1(III), when denatured in dithiothreitol. These results suggest that the original, extracted protein consisted primarily of a precursor form of type III collagen. This procollagen did not polymerize when heated at 37°C and did not form the usual segment long spacing aggregates under suitable conditions. It was not modified by incubation with a purified procollagen peptidase preparation. This appears to be the first example of the isolation of type III (pro)collagen by extractive methods, without resorting to tissue digestion by proteolytic enzymes.