TRANSITION-METALS AS PROTEASE INHIBITORS

An alternative approach to the development of clinically useful protea se inhibitors was investigated. The approach utilized coordination che mistry of transition metal ions rather than substrate analogs to block active sites of these enzymes. In the case of serine proteases it was found that aqueous Ti(IV) is a potent inhibitor of the trypsin subcla ss, but not the chymotrypsin subclass. The direct binding of Ti(IV) to trypsin was made possible by the presence of a free carboxyl group at the bottom of the substrate binding pocket of the enzyme, and the fiv e-coordinate geometry of TiO(SO4)(H2O). Although initial binding of Ti (IV) was reversible, it was followed in time by irreversible inhibitio n. Direct binding of octahedral or tetrahedral metal ion complexes was prevented by the inability of the enzyme active sites to promote form ation of a five-coordinate transition state of the metal ion required for reaction. These studies demonstrate the ability of direct metal io n binding as a way to enhance blocking of enzyme active sites as compa red with that of traditional organic inhibitors. Application of these findings was investigated by measuring the affect Ti(IV) had on growth of Escherichia coli, Salmonella typhimurium, and Pseudomonas aerugino sa. Five-coordinate titanyl sulfate completely inhibited the growth of these organisms. This suggests that five-coordinate titanyl sulfate, which is easier and less expensive to manufacture than conventional an tibiotics, may be useful in controlling endemic infections of E. coli and S. typhimurium.