Procollagen C-endopeptidase

This chapter examines the activity, specificity and structural chemistry of procollagen C-endopeptidases (PCP). PCP cleaves the carboxyl propeptides of procollagens I, II and III, and those of the respective pC-collagens. The sequences surrounding the scissile bonds within the various substrates show a considerable degree of variability, and have been difficult to define a unique consensus cleavage site for PCP. PCP activity can be assayed with [3H]tryptophan-labeled type I procollagen, in which almost all of the radioactivity is in the C-propeptide or procollagen labeled throughout the pro-α chains with a mixture of [14C] amino acids. The pH optimum of PCP is 8–8.5 and the enzyme requires calcium for activity. The level of PCP in natural sources is very low. Microgram amounts of the enzyme have been purified from media of organ cultures of chick embryo tendons and media of cultured mouse 3T6 fibroblasts with corresponding purification factors of 21,000 and 18,000. The enzyme isolated from chick apparently represents the mTld variant, whereas the mouse fibroblast enzyme corresponds to BMP-1. The purification protocol that worked for isolation of the chick enzyme has also been used to purify human PCP from the culture medium of MG63 cells.