Arginine residue(S) at the active site(S) of the nitrate reductase complex from Amaranthus

Abstract

Chemical modification of nitrate reductase (NR) from Amaranthus dubious leaves with either phenylglyoxal or 2,3-butanedione reduces the catalytic activity of the enzyme complex. The kinetics of the reaction in the presence of either reagent indicates a rapid partial inactivation followed by a slower rate of inactivation which leads eventually to completely inactive enzyme. NADH-NR and the FMNH₂-NR activities of the NR complex are inactivated at a faster rate as compared to the NADH dehydrogenase activity. NADH protected the slower phase of inactivation of NADH-NR and NADH dehydrogenase but the rapid phase of inactivation could not be prevented by any of the ligands tested. The inactivation of FMNH₂-NR could not be prevented by any compound tested. The data suggest that NR contains active site arginine residue(s) that are involved in NADH binding site of the enzyme. Arginine modification also affects the partial activity associated with the molybdenum containing moiety, i.e. FMNH₂-NR.