Glutamate dehydrogenase activity in developing soybean seed: Kinetic properties of three forms of the enzyme

Abstract

The kinetic parameters of three forms of glutamate dehydrogenase from developing soybean seed have been determined. For all enzymes double reciprocal plots were intersecting in animating and deaminating directions when each substrate was held at a fixed concentration in turn. In amination all plots were linear and the K NH4 + and K NAD(P)H values determined using (NH 4) 2SO 4 were about one-fifth of values obtained with NH 4CL. In deamination, plots were linear when l-glutamate and NADP + were varied and biphasic with varied NAD +. It was not possible to determine the mechanisms of the enzymes but the data are consistent with nucleotide binding to the free enzyme forms. The role of the enzymes in the tissue is discussed. They could be active in deamination in the later stages of seed development when the supply of carbohydrate could be limiting. They could also be important in ammonia assimilation and their kinetic properties are discussed in relation to known properties of glutamine synthetase and glutamate synthase and cellular levels of enzyme substrates.