Kinetic Studies on the Interaction of α1-Proteinase Inhibitor (Pittsburgh) with Trypsin-Like Serine Proteinases

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Abstract
The rates of interaction of a number of serine proteinases with a mutant form of .alpha.1-proteinase inhibitor (referred to as .alpha.1-proteinase inhibitor (Pittsburgh)), in which a methionine-358 to arginine-358 mutation has occurred, have been determined. An approximately 6000-fold increase in the second order association rate constant with human thrombin was observed (48 M-1 .times. s-1 for the normal protein to 3.1 .times. 105 M-1 .times. s-1 for the arginine mutant), confirming previously observed data using bovine thrombin (Owen, M.C. Brennan, S.O., Lewis, J.H. and Carrell, R.W. (1983) New England J. Med. 309. 694-698). However, substantial increases in the rates of association with other trypsin-like enzymes were also noted, indicating that the replacement of methionine by a basic residue affects all serine proteinases with this kind of specificity. There was a marked decrease in the rates of interaction of the Pittsburgh mutant with both human neutrophil elastase and porcine pancreatic elastase, the inhibitor being converted into lower molecular mass fragments after interaction with either enzyme. Butanedione caused a substantial loss in the inhibitory activity of the arginine mutant, while having no effect on the normal protein. These data, when compared to those previously reported for differences in reaction rates between normal and oxidized .alpha.1-proteinase inhibitor (Beatty, K., Bieth, J. and Travis, J. (1980) J. Biol. Chem. 255, 3931-3934), are consistent with the interpretation that the amino acid in the P1-position at the reactive site of this protein has a marked effect on determining its primary specificity.

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