The hydride-donation reaction of reduced nicotinamide adenine dinucleotide. 2. MINDO/3 and STO-3G calculations on the role of the carbamoyl group in enzymic reactions

The enzyme-catalyzed stereospecific hydride-transfer equilibrium RH + NAD’ R+ + NADH has been studied with the help of semiempirical (MIND0/3) and ab initio (STO-3Gc)a lculations on corresponding model compounds. It seems possible to relate the stereospecificity simply to an out-of-plane orientation of the CONH2 group in the transition state of the reaction. One of the important functions of the enzyme would be to freeze the otherwise almost freely rotating CONHz group in a favorable orientation.