The synthesis of inhibitors for processing proteinases and their action on the Kex2 proteinase of yeast

Peptidyl chloromethane and sulphonium salts containing multiple Arg and Lys residues were synthesized as potential inhibitors of prohormone and pro-protein processing proteinases. The potencies of these compounds were assayed by measuring the kinetics of inactivation of the yeast Kex2 proteinase, the prototype of a growing family of eukaryotic precursor processing proteinases. The most potent inhibitor, Pro-Nvl-Tyr-Lys-Arg-chloromethane, was based on cleavage sites in the natural Kex2 substrate pro-alpha-factor. This inhibitor exhibited a Ki of 3.7 nM and a second-order inactivation rate constant (k2/Ki) of 1.3 x 10(7) M-1.s-1 comparable with the value of kcat./Km obtained with Kex2 for the corresponding peptidyl methylcoumarinylamide substrate. The enzyme exhibited sensitivity to the other peptidyl chloromethanes over a range of concentrations, depending on peptide sequence and alpha-amino decanoylation, but was completely resistant to peptidyl sulphonium salts. Kinetics of inactivation by these new inhibitors of a set of ‘control’ proteinases, including members of both the trypsin and subtilisin families, underscored the apparent specificity of the compounds most active against Kex2 proteinase.