alpha-Chymotryptic hydrolysis of derivatives of the specific substrates with substituents in the nucleus.

Steady state kinetic studies of alpha-chymotrypsin [EC 3.4.21.1]-catalyzed hydrolysis of nucleus-substituted derivatives of the specific substrates were made at pH 6.5 and 7.8. Ac-Trp(NCps)-OMe was hydrolyzed more readily than Ac-Trp-OMe owing to its smaller Km value. The kcat values of Ac-Trp(CHO)-OMe and Ac-Tyr(3-no2)-ome were higher than those of the corresponding unmodified substrates, suggesting that derivatives with a substituent as large as a formyl or nitro group at the epsilon-position are stereochemically favorable to the catalytic process. Derivatives of Ac-Phe-OMe with a chain of four atoms at the 3 or 4-position of the phenyl nucleus and 2,3-dihydropyrrolo[2,3-b]indoles derived from Ac-Trp-OMe were not hydrolyzed at all.