TRYPSIN COMPLEXED WITH ALPHA(1)-PROTEINASE INHIBITOR HAS AN INCREASEDSTRUCTURAL FLEXIBILITY

Mutant rat trypsin Asp(189)Ser was prepared and complexed with highly purified human alpha(1)-proteinase inhibitor. The complex formed was p urified to homogeneity and studied by N-terminal amino acid sequence a nalysis and limited proteolysis with bovine trypsin. As compared to un complexed mutant trypsin, the mutant enzyme complexed with alpha(1)-pr oteinase inhibitor showed a highly increased susceptibility to enzymat ic digestion. The peptide bond selectively attacked by bovine trypsin was identified as the Arg(117)-Val(118) one of trypsin. The structural and mechanistic relevance of this observation to serine proteinase-su bstrate and serine proteinase-serpin reactions are discussed.