Kinetic mechanism of NADH-dependent glutamate synthase from lupin nodules.

From initial-rate studies, a partially random kinetic mechanism has been deduced for NADH-dependent glutamate synthase from lupin nodules. The mechanism involves compulsory binding of NADH as first substrate, followed by random-order binding of glutamine and 2-oxoglutarate. Patterns of inhibition by glutamate substantiate the mechanism. Dithionite was incapable of acting as an alternative reducing substrate although it is known to reduce the flavine groups of the enzyme. The implications of these results are discussed. Published rate equations for this type of mechanism were found to be unsatisfactory for this enzyme and suitable new equations are produced. These equations should have general application where the obligatory first substrate binds very tightly.