ISOLATION AND PARTIAL CHARACTERIZATION OF THE CARBOXY-TERMINAL PROPEPTIDE OF TYPE-II PROCOLLAGEN FROM CHICK-EMBRYOS

The carboxy-terminal propeptide from type II procollagen was isolated from organ cultures of sternal cartilages from 17-day-old chick embryos. The procedure provided the 1st isolation of the carboxy-terminal propeptide in amounts adequate for chemical characterization. The propeptide was isolated as a disulfide-linked trimer with an apparent MW of about 100,000. After reduction, monomers of about MW 34,000 were obtained. Antibodies were prepared to the propeptide and used to establish its identity. The antibodies precipitated type II procollagen but did not precipitate type II procollagen from which the amino- and carboxy-terminal propeptides were removed with pepsin. No collagen-like domain was found in the propeptide, and the amino acid composition was similar to that of globular proteins. The circular dichroism spectrum of the propeptide suggested the presence of .beta.-structure together with some random-coil structure. The type II carboxyterminal propeptide is similar to the 2 different carboxyterminal propeptides of type I procollagen in amino acid composition, molecular size, optical properties and antigenicity. The homology among the type I and type II carboxy-terminal propeptides is consistent with the current hypothesis that they serve similar functions in vivo. The differences in structure may account for the selection of the appropriate pro.alpha. chains to form the correct trimers in cells synthesizing several types of pro.alpha. chains simultaneously.