Hydrogen exchange kinetics of bovine pancreatic trypsin inhibitor .beta.-sheet protons in trypsin-bovine pancreatic trypsin inhibitor, and trypsinogen-bovine pancreatic trypsin inhibitor, and trypsinogen-isoleucylvaline-bovine pancreatic trypsin inhibitor

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Abstract
Hydrogen exchange rates of six .beta.-sheet peptide amide protons in bovine pancreatic trypsin inhibitor (BPTI) have been measured in free BPTI and in the complexes trypsinogen-BPTI, trypsinogen-Ile-Val-BPTI, bovine trypsin-BPTI, and porcine trypsin-BPTI. Exchange rates in the complexes are slower for Ile-18, Arg-20, Gln-31, Phe-33, Tyr-35, and Phe-45 NH, but the magnitude of the effect is highly variable. The ratio of the exchange rate constant in free BPTI to the exchange rate constant in the complex, k/kcplx, ranges from 3 to .mchgt. 103. Gln-31, Phe-45, and Phe-33 NH exchange rate constants are the same in each of the complexes. For ILe-18 and Tyr-35, k/kcplx is .mchgt. 103 for the trypsin complexes but is in the range 14-43 for the trypsinogen complexes. Only the Arg-20 NH exchange rate shows significant differences between trypsinogen-BPTI and trypsinogen-Ile-Val-BPTI and between porcine and bovine trypsin-BPTI.
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