Kinetics of Inactivation of NADP+-Linked Isocitrate Dehydrogenase from Germinating Mung Bean (Vigna radiata)

Abstract

Metal chelating agent EDTA inhibits the activity of mung-bean NADP+-linked isocitrate dehydrogenase (ICDH) in a competitive manner. The activity of the Apo-enzyme was restored by divalent metal ions with the order of effectiveness found to be Mn 2+> Mg2+ > Zn2+ > Co2+ > Cu2+. here appeared to be a single type of metal binding site that was saturated either with 0.5 mM of Mn2+ or with 2.5 mM of Mg2+. ADP, ATP and NADPH inhibit the enzyme in competitive manner. On titration with 5, 5’-dithiobis (2-nitrobenzoate), i.e. DTNB, the mung bean isocitrate dehydrogenase showed 4.0 reactive -SH groups per molecule. The denatured ICDH enzyme of mung bean possess 8.1-SH groups per molecule. The blocking of this group with -SH reagents, lead to the inactivation of mung bean ICDH enzyme. Time-dependent inactivation of ICDH with iodoacetamide and Nethylmaleimide (NEM) revealed decay in the activity in a single exponential manner.