INHIBITION OF PORCINE PANCREAS KALLIKREIN BY DI-ISOPROPYL-FLUOROPHOSPHATE - KINETICS, STOICHIOMETRY, AND NATURE OF GROUP PHOSPHORYLATED

The bimolecular velocity constant of the irreversible inhibition of porcin pancreas kallikrein by di‐isopropyl‐fluorophosphate was determined as 8 ± 1 1 × mole−1× min−1 at pH 7.2 and 25° From the pH dependency of the reaction rate an absolute requirement for an ionized group in the enzyme, whose conjugate acid has a pKa of 6.85, is inferred. The velocity of the inhibition is reduced in the presence of substrate. In the course of the inhibition process at least a part of the di‐isopropyl‐fluorophosphate molecule, comprising the phosphorus atom, is incorporated into the enzyme in a ratio of one residue per inhibited kallikrein molecule. The reaction product shows stability against hydrolysis by dilute acid comparable to the stability of di‐isopropyl‐phosphoryl‐trypsin. After acid hydrolysis, part of the phosphorus is found in a compound which cochromatographs with serine phosphate in several solvents. Pancreas kallikrein may consequently be added to the group of the so‐called “serine hydrolases”. Copyright © 1969, Wiley Blackwell. All rights reserved