Kinetic Ramifications of the Association-Dissociation Behavior of NAD Malic Enzyme : A Possible Regulatory Mechanism.

NAD malic enzyme can exist in dimer, tetramer, or octamer form. Freshly prepared enzyme from Solanum tuberosum var. Chieftan exists predominantly as the octamer and during storage is progressively converted into lower molecular weight forms. High ionic strength favors dimer formation, whereas high concentrations of malate or citrate favor tetramer formation. The tetramer is the most active form, having a low K(m) for malate and a high V(max). The dimer, with its high K(m) and low V(max), is the least active form. Malate may regulate NAD malic enzyme by controlling its state of oligomerization.