Kinetic properties of NAD-dependent glyceraldehyde-3-phosphate dehydrogenase from the host fraction of soybean root nodules.
The kinetic mechanism of NAD-dependent glyceraldehyde-3-phosphate dehydrogenase [D-glyceraldehyde-3-phosphate:NAD+ oxidoreductase (phosphorylating), EC 1.2.1.12] from the host cytosolic fraction of soybean (Glycine max L. Merr. cv. Williams) root nodules has been investigated by steady-state initial velocity studies and inhibition studies with products and product analogs. The results were consistent with the enzyme having a bi-uni-uni-uni ping-pong mechanism in which NAD+ and phosphate interacted sequentially with the enzyme, followed in turn by the release of 1,3-bisphosphoglycerate, the addition of D-glyceraldehyde-3-phosphate, and the release of NADH. At pH 7.2, NAD+ bound to the enzyme in a rapid-equilibrium fashion, whereas at pH 8.8 there was rapid-equilibrium addition of both NAD+ and phosphate to the enzyme. NADH was a strong competitive inhibitor with respect to NAD+ and phosphate. The enzyme was very labile, especially above pH 8, but the rate of loss of activity was considerably reduced in the presence of NAD+ and phosphate. The possible role of these properties in the regulation of NAD-dependent glyceraldehyde-3-phosphate dehydrogenase in the host cytosol of soybean nodules is discussed.
Department of Agricultural Chemistry and Soil Science, University of Sydney, New South Wales, Australia.
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D000249:Adenosine Monophosphate / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology*; D005986:Glyceraldehyde 3-Phosphate / Q000378:metabolism; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D008956:Models, Chemical; D009243:NAD / Q000378:metabolism; D009586:Nitrogen Fixation / Q000502:physiology; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010710:Phosphates / Q000378:metabolism; D013025:Glycine max / Q000201:enzymology*; D013559:Symbiosis / Q000502:physiology*
D010710:Phosphates; D009243:NAD; D005986:Glyceraldehyde 3-Phosphate; D000249:Adenosine Monophosphate; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases