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. The polysomal system is activated by a salt extract of reticulocyte ribosomes and is inhibited by aurintricarboxylic acid, suggesting that the polysomes are able to initiate protein synthesis.