INHIBITION OF BOVINE CATHEPSIN-L AND CATHEPSIN-S BY STEFINS AND CYSTATINS

Inhibition of bovine cathepsins L and S by bovine stefin B, human stef ins A and B and cystatin C was studied under pseudo-first-order condit ions by continuous fluorimetric assay. All inhibitors formed very tigh t complexes with the enzymes (K-i less than or equal to 29 pM). The bi nding was reversible (k(diss) = 0.52-16.7 x 10(-4) s(-1)) and very fas t (k(ass) = 2.8-6.2 x 10(7) M(-1) s(-1)). Cystatin C was the strongest inhibitor of the enzymes, but the affinity was too tight to be measur ed accurately by this method. Consistently weaker inhibition of cathep sin S by all the stefins is apparent due mainly to the higher dissocia tion rate constants.