EFFECTS OF TEMPERATURE ON STEREOCHEMISTRY OF ENZYMATIC-REACTIONS

A brief discussion of the theoretical basis for effects of temperature on stereoselectivity of enzyme catalysed reactions is presented. In t heory, the stereoselectivity of an enzymatic reaction can either incre ase or decrease as the reaction temperature is raised. The secondary a lcohol dehydrogenase from Thermoanaerobacter ethanolicus reduces 2-but anone to (R)-2-butanol at 37 degrees C, with increased stereoselectivi ty at higher temperatures and in the presence of NADP analogues. In co ntrast, at 37 degrees, 2-pentanone and 2-hexanone are reduced to (S)-2 -pentanol and (S)-2-hexanol, respectively, but the stereoselectivity d ecreases at higher temperatures and in the presence of NADP analogues. Reduction of racemic 2-methylbutanal by the primary alcohol dehydroge nase from T. ethanolicus gives (S)-2-methyl-1-butanol with greater ste reospecificity at 35 degrees (51% e.e.) than at 15 degrees (14% e.e.). Horse liver alcohol dehydrogenase shows a preference for oxidation of the (S)-enantiomers of acyclic secondary alcohols at 25 degrees, with a decrease in stereospecificity at higher temperatures.