A study of proteinase inhibition by simulation of inhibitor reactive site regions: interaction of the C-terminal undecapeptide of ovein prolactin with some proteinases.

The C-terminal undecapeptide of ovine prolactin, H-Leu-Asn-Cys-Arg-Ile-Ile-Try-Asn-Asn-Asn-Cys-OH possesses several structural features common to protein proteinase inhibitors, yet has no inhibitor properties. The undecapeptide is completely hydrolysed by trypsin (Arg-Ile bond) and by chymotrypsin (Tyr-Asn bond), with a proteolytic coefficient of approximately 3,000 M-1 sec-1 and 240 M-1 sec-1 respectively. On the basis of these results, a consideration of entropy, and studies by other workers, we agree with the view of Nishino et al. that the best models for small synthetic peptides with inhibitor properties would be those naturally-occurring inhibitors whose reactive site is located within a small disulphide loop.