INTERACTION OF SUBTILISINS WITH SERPINS

Serpins are well-characterized inhibitors of the chymotrypsin family s erine proteinases. We have investigated the interaction of two serpins with members of the subtilisin family, proteinases that possess a sim ilar catalytic mechanism to the chymotrypsins, but a totally different scaffold. We demonstrate that alpha(1)proteinase inhibitor inhibits s ubtilisin Carlsberg and proteinase K, and alpha(1)antichymotrypsin inh ibits proteinase K, but not subtilisin Carlsberg. When inhibition occu rs, the rate of formation and stability of the complexes are similar t o those formed between serpins and chymotrypsin family members. Howeve r, inhibition of subtilisins is characterized by large partition ratio s where more than four molecules of each serpin are required to inhibi t one subtilisin molecule. The partition ratio is caused by the serpin s acting as substrates or inhibitors. The ratio decreases as temperatu re is elevated in the range 0-45 degrees C, indicating that the serpin s are more efficient inhibitors at high temperature. These aspects of the subtilisin interaction are all observed during inhibition of chymo trypsin family members by serpins, indicating that serpins accomplish inhibition of these two distinct proteinase families by the same mecha nism.