Energetics of proline racemase: transition-state fractionation factors for the two protons involved in the catalytic steps.

摘要: The isotope effects for the interconversion of L-proline and D-proline, catalyzed by proline racemase, have been determined in saturated region with both [2-2H]proline [2-3H]proline. deuterium fractionation factors each protons flight obtained from two kinds experiment: measuring rate racemization one enantiomer as it racemizes into an equilibrated pool unlabeled content a sample at optical rotation maximum that occurs when equimolar mixture deuterium-labeled other runs to equilibrium. tritium measurements loss solvent [2-3H]proline Good agreement is found among method. are not identical: proton derived 0.375 D-proline 0.44. This difference has confirmed double-competition experiment which DL-[2-2H]proline DL-proline followed time. (initially zero) passes through maximum, ratio (0.86) obtained. These data, coupled equilibrium factor 2-position (which be 1.17), provide transition-state in-flight protons, delineate nature transition state(s) enzyme-catalyzed racemization.