Hydrogen-tritium exchange kinetics of soybean trypsin inhibitor (Kunitz). Solvent accessibility in the folded conformation.

摘要: The hydrogen exchange kinetics of Kunitz soybean trypsin inhibitor (STI) has been studied at pH 2, 3, and 6.5. From the temperature dependence proton low pH, THE CONTRIBUTION OF MAJOR, REVERSIBLE PROTEIN UNFOLDING To determined. Exchange directly from folded conformation is characterized by an apparent activation energy (E*app) approximately 25 kcal/mol, close to that chemical step. At 6.5 protein more stable than all but congruent 8 protons can be observed with E*app 27 kcal/mol. This implies are accessible solvent in solution structure STI. Estimates made average number water molecules per molecule STI consistent a accessibility model kinetics. These estimates indicate very few within matrix necessary explain data. Calculations done for 30 degrees, approximating sphere radius = 18 A. calculations 4 shell 13 16 center molecule, while less 1 indicated innermost also suggest there 190 associated outermost 1.5-2 A sphere. While these values hydrophobic region central matrix, they outer 1/3 static X-ray coordinates. Our results any movements or fluctuations responsible processes localized regions globular structure.