Analogues of acetyl chymotrypsin.

Previous papers (1, 2) have reported the acylation of chymotrypsin with several nitrophenyl acetates. It was of obvious interest to test the behavior of nitrophenyl esters of other acids in the same connection. It now appears that chymotrypsin may be acylated by a number of acids differing considerably from acetic acid in structure. Beneoyl and salicyl chymotrypsins were prepared and found to resemble the acetyl derivative rather closely in so far as they were examined. On the other hand, hippuryl chymotrypsin forms and decomposes so rapidly that we have been unable to work with it. The stability, as well as the rate of formation of the acylated enzyme, has thus been found to vary with the nature of the acyl group, as might be expected if the acylated enzyme does indeed correspond to an intermediate in normal enzyme catalysis. A somewhat similar effect appears in the transesterification reaction of chymotrypsin (3), in that isobutyl and tert-butyl alcohols react very slowly in comparison to their straight chain analogues. Our attention was thus directed to the acids corresponding to those alcohols, namely isobutyric and trimethylacetic acids.