THE MECHANISTIC AND EVOLUTIONARY BASIS OF STEREOSPECIFICITY FOR HYDROGEN TRANSFERS IN ENZYME-CATALYZED PROCESSES

The origin of stereospecificity in enzyme-catalysed processes is attri buted to either mechanistic imperatives or to the evolutionary origin of an enzyme, Recent analysis of the syn-anti dichotomy for hydratase- dehydratase enzymes has clearly demonstrated that it is a historical c ontingency that has played a significant role in determination of ster eospecificity, Historical contingencies also appear to play a signific ant role in (a) the selection of one out of a possible eight different stereochemical courses available for an enoyl thioester reductase, an d (b) the discrimination between diastereotopic hydrogens in coenzyme B-12-dependent rearrangements.