[Kinetic characteristics of methionine sulfoxide-thermitase]

For methionine sulfoxide(226)-thermitase the kinetic parameters Km and kcat were determined with p-nitrophenyl acetate and Suc-dialanyl-phenylalanyl 4-nitroanilide as substrates. A drastic decrease in the catalytic rate but only small changes in the substrate affinity were observed in comparison to the native enzyme. Also with the high-molecular weight substrate casein the affinity remained unaffected whereas the catalytic rate was diminished to one-half only. The Ki for the reversible inhibitors phenylboronic acid and Z-dialanyl-phenyl-alanine methyl ketone showed only small changes.