Oxidized and Met358-->Leu mutated alpha 1-proteinase inhibitor as substrates of Pseudomonas aeruginosa elastase.

This paper investigates the catalytic activity of Pseudomonas aeruginosa elastase using the bait region of the alpha 1-proteinase inhibitor as a substrate. The bacterial enzyme cleaves the Pro357-Met358 bond of the wild-type inhibitor and the recombinant Met358 inhibitor and the Pro357-Leu358 bond of the recombinant Met358-->Leu inhibitor with kcat/Km values of 9 x 10(4) M-1 s-1, 1.4 x 10(5) M-1 s-1 and 3.5 x 10(5) M-1 s-1, respectively. In contrast, the N-chlorosuccinimide-oxidized inhibitor (Met351 and Met358 = methionine sulfoxides) is cleaved at the Glu354-Ala355 position with a significantly lower rate (kcat/Km = 10(4) M-1 s-1). The pH optimum for the cleavage of the native, the oxidized, the Met358-->Leu mutated inhibitor, and 2-aminobenzoyl-Ala-Gly-Leu-Ala-4-nitrobenzylamide, a synthetic Pseudomonas elastase substrate are, 6.0, 7.0, 6.5 and 5.8, respectively. We conclude that P. aeruginosa elastase readily hydrolyzes substrates with P'1 methionine or alanine residues and that its pH optimum is not as alkaline as usually thought.