No description available.

Stopped-flow experiments in which the NAD-malic enzyme was preincubated with different reactants at near saturating substrate concentrations suggest a slow isomerization of the E:NAD:Mg complex. The lag is eliminated by preincubation with Mg˙² and malate suggesting that the formation of E:Mg:Malate either bypasses or speeds up the slow isomerization step. Circular dichroic spectral studies of the secondary structural changes of the native enzyme in the presence and absence of substrates supports the existence of conformational changes with NAD˙ and malate. Thus, a slow conformational change of the E:NAD:Mg complex is likely one of the rate-limiting steps in the pre-steady state.