INHIBITION OF HUMAN-LEUKOCYTE AND PORCINE PANCREATIC ELASTASE BY HOMOLOGS OF BOVINE PANCREATIC TRYPSIN-INHIBITOR

The interactions of three BPTI homologues with human leukocyte elastas e and porcine pancreatic elastase have been investigated. The principa l mutation in determining the specificity of inhibition was the Lys(15 )-Val mutation at the P-1 position. An additional mutation at P-3, i.e ., BPTI (Lys(15)Val, Pro(13)-Ile), increased the inhibition of HLE to a K-i = 2.5 x 10(-10) M, but decreased the inhibition of PPE, showing this to be a useful site for improving selectivity. Kinetic evidence s uggests that the inhibition of HLE by BPTI homologues probably takes p lace by a two-step mechanism in which an isomerization step occurs aft er initial binding. H-1 NMR spectroscopy of the BPTI (Lys(15)-Val) and BPTI (Lys(15)-Val, Pro(13)-Ile) mutants indicates that small conforma tional changes are associated with the mutations, but these are locali zed in the immediate vicinity of the mutation in the outer binding loo p and in the inner loop connected to it through the Cys(14)-Cys(38) di sulfide bridge.