Isotope Effects on Hydride Transfer between NAD+ Analogues

Article abstract of DOI:10.1021/ja00364a026

Primary kinetic hydrogen isotope effects (KIE's) for hydride transfer between NAD⁺ analogues are between 6 and 4, for reactions with equilibrium constants ranging from 0.7 to 10¹⁶.There is no sign of the sharp change in KIE which would signal the change of a rate-limiting step in a multistep mechanism, and other evidence also indicates a one-step mechanism. ² The secondary KIE produced by changing the hydrogen already attached at the acceptor site from H to D is about 10percent smaller when the transferred atom is D than when it is H.These results, combined with the values of the primary KIE's, strongly suggest some nuclear tunneling in the reaction coordinate.