Mechanism of inhibition of pepsin by pepstatin. II.

Pepstatin, a strongly bound inhibitor of acid proteases, does not instantaneously bind to pepsin. The dissociation constant of pepsin-pepstatin complex is 9.7×10-11 M using Phe・Gly・His・Phe(NO2)・Phe・Ala・PheOMe as substrate. Difference ultraviolet absorption spectra show conformational change of pepsin in interaction with pepstatin. The bindillg of pepsin with pepstatin is stoicheometric and the normality of pepsin can be easily titrated by pepstain. Pepsin modified by 1,2-epoxy-3-(p-nitrophenoxy)