TEMPERATURE-DEPENDENCE OF THE PRIMARY KINETIC ISOTOPE EFFECT IN HYDRIDE TRANSFER-REACTIONS WITH NAD(+) AND NADH MODELS

,6-dichlorobenzyl)-1,4-(H-1(2))dihydronicotinamide and 6-dichlorobenzy l)-1,4-(H-1,H-2)dihydronicotinamide were oxidized with nitrosobenzene (NOB), 2,6-dichloroindophenol (DCPIP), 2,4,6-trinitrobenzenesulfonic a cid (TNBS), 10-methyl-acridinium ion (MAI), and 10-methyl-9-phenyl-acr idinium ion (MPAI). In addition, 2-propanol-h(g) and 2-propanol-d(8) w ere oxidized by NAD(+) in the presence of yeast alcohol dehydrogenase. Investigation of the temperature dependence of the kinetic isotope ef fect indicated that the redox reactions with MAI and MPAI have very si milar thermodynamic characteristics and proceed via a linear transitio n state. Redox reactions with NOB, DCPIP, and TNBS have entirely diffe rent thermodynamic characteristics, and probably proceed via a differe nt transition state. Thermodynamic characteristics of enzymatic reacti on are very similar to model redox reactions with MAI and MPAI. (C) 19 97 Academic Press.