Inhibition of trypsin by t-Butyloxycarbonyl-α-aza-(4-aminophenyl)alanine phenyl ester

T-Butyloxycarbonyl-α-aza-(4-aminophenyl)alanine phenyl ester (Fig. 1, III: R = NH₂) has been synthesized. The rate of inhibition of trypsin (EC 3.4.21.4) by this compound (due to acylation followed by slower deacylation) shows a marked pH maximum at approximately 6. The shape of the pH—rate curve is discussed in terms of (i) the normal pH—activity curve of trypsin reacting with a charged substrate, i.e. the protonated form of the amino compound, (ii) the deprotonation of the 4-amino group with pK_a 4·3, and (iii) the lower rate of reaction of the enzyme with the uncharged, deprotonated form of the ester.