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 theory, the stereoselectivity of an enzymatic reaction can either increase or decrease as the reaction temperature is raised. The secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus reduces 2-butanone to (R)-2-butanol at 37 degrees C, with increased stereoselectivity at higher temperatures and in the presence of NADP analogues. In contrast, at 37 degrees, 2-pentanone and 2-hexanone are reduced to (S)-2-pentanol and (S)-2-hexanol, respectively, but the stereoselectivity decreases at higher temperatures and in the presence of NADP analogues. Reduction of racemic 2-methylbutanal by the primary alcohol dehydrogenase from T. ethanolicus gives (S)-2-methyl-1-butanol with greater stereospecificity 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.