In vitro synthesis of procollagen on polysomes.

The major collagenous products synthesized in a cell-free polysome preparation are pro-alpha1 and pro-alpha2, formed in a ratio of 2:1. They are the precursor forms of alpha1 and alpha2 chains of normal connective-tissue collagen that are also formed in small amounts. A procollagen peptidase activity has been demonstrated in the supernatant fraction that can account for the formation of alpha1 and alpha2 chains from their precursors.

Procollagen peptidase: an enzyme excising the coordination peptides of procollagen.

A heritable connective tissue disorder of cattle, dermatosparaxis, is characterized by an extreme fragility of the skin and the presence of additional peptides at the N-terminal extremities of the collagen alpha chains, p-alpha(1) and p-alpha(2). The existence of an enzyme activity is demonstrated in normal connective tissues that is capable of cleaving these additional N-terminal peptides from dermatosparaxic collagen. The activity is demonstratable with dermatosparaxic collagen in solution, as well as with reconstituted dermatosparaxic collagen fibrils polymerized in vitro.