Characterization of the Pro-α1 Chain of Procollagen

Embryonic chick calvaria (cranial bones) were cultured in the presence of [35S]cysteine and labeled procollagen, a collagen precursor, was isolated. Incorporation of the 35S label in the pro-α1 chain of procollagen permitted its use as a relatively specific marker for the chain during purification, since neither the α1 nor the α2 chain of collagen contains cysteine. Determinations of the molecular weight of pro-α1 by calibrated molecular sieve chromatography and sodium dodecyl sulfate-acrylamide gel electrophoresis indicated a value of 115,000 in good agreement with previous estimates using [3H]proline-labeled chains. Collagenase digestion of [35S]cysteine- and [3H]proline-labeled pro-α1 chains revealed that the additional non-triple helical sequence of the precursor chain is divided into (a) collagenase-resistant regions which contain cysteine and little or no proline and (b) collagenase-susceptible regions lacking cysteine and containing proline but not hydroxyproline. Amino acid analysis of the pro-α1 chain confirmed the presence of 5 or 6 half-cystines per chain and revealed a composition which differs considerably from that of collagen.