[Catalytic mechanism of dipeptidyl-peptidase IV]

Dipeptidyl-peptidase IV isolated from pig kidney microsomes catalyses hydrolysis in a number of dipeptidylaryl-amides of types L-AS-L-Ala-R and L-AS-L-Pro-R. Kinetic studies involving two competing substrates suggest the probable existence of a catalytic centre for both groups of substrates. The speed-determining steps in enzymatic hydrolysis differ in the order L-AS-L-Pro-R and L-AS-L-Ala-R. The secondary enzymatic deuterium-isotopic effects in the hydrolysis of L-Ala-L-Ala-2-d1-pNA are fixed at KHM/KDM = 1.24 and VHmax/VDmax = 1.27. The existence of an acyl-enzyme mechanism is considered likely.