A sensitive new substrate for chymotrypsin.

A new substrate for chymotrypsin, succinyl-Ala—Ala—Pro—Phe- p -nitroanilide has been synthesized. Kinetic analysis of the hydrolysis of this peptide by bovine chymotrypsin gave a K m of 0.043 m m and a k cat of 45 s −1 . This substrate is readily soluble and stable to hydrolysis in Tris buffer at pH 8. Chymotrypsin levels down to 1.0 ng can be rapidly determined spectrophotometrically.