PDB-2kai: REFINED 2.5 ANGSTROMS X-RAY CRYSTAL STRUCTURE OF THE COMPLEX FORMED BY PORCINE KALLIKREIN A AND THE BOVINE PANCREATIC TRYPSIN INHIBITOR. CRYSTALLIZATION, PATTERSON SEARCH, STRUCTURE DETERMINATION, REFINEMENT, STRUCTURE AND COMPARISON WITH ITS COMPONENTS AND WITH THE BOVINE TRYPSIN-PANCREATIC TRYPSIN INHIBITOR COMPLEX