An MO cavity model of enzyme catalysis: Semiempirical calculations of reaction courses of acetaldehyde reduction and ethanol oxidation by an NAD model

Abstract

General suggestions concerning the possibility to interpret the elementary reaction steps in biocatalytic processes, as if proceeding in pseudovacuum of a protein cavity, have been presented. The approach is illustrated by MNDO investigation of the interaction of 1-methyl-1,4-dihydronicotinamide (II) with acetaldehyde or its protonated species Ia and Ib, respectively. The preactivation step Ia → Ib has been shown to accelerate the interconversion of substrate Ib into ethanol and 3-aminocarbonylpyridinium (V) more effectively than a subsequent protonation of the possible 1,6-dihydropyridine intermediate III arising from Ia and II. The opposite reaction path of V with ethanol and ethoxide is also being examined.