High resolution nuclear magnetic resonance studies of the active site of chymotrypsin. II. Polarization of histidine 57 by substrate analogues and competitive inhibitors.

摘要: Abstract The proton nuclear magnetic resonance signal of the His57-Asp102 hydrogen bonded in charge relay system chymotrypsinogen A and chymotrypsin δ has been monitored to determine influence substrate analogues competitive inhibitors on electronic state active site regions. Borate ion, benzene boronic acid 2-phenylethylboronic acid, when bound at pH 9.5 shift position His-Asp −15.9, −16.3 −17.2 parts per million, respectively. These positions are intermediate between low free enzyme −18.0 million high −14.9 million. presence these prevents from titrating region 6 9.5. Similar field shifts observed for subtilisin BPN′ complexed with acids. results support chemical crystallographic data which show that negatively charged tetrahedral adducts formed sites enzymes. When combined similar binding N -acetyl- l -tryptophan , they suggest a direct interaction occurs histidine atom occupying leaving group substrate, presumably bond. was also complexes bovine pancreatic trypsin inhibitor over range 4 9. In complex had 9 indicating His57 is neutral form, pH.