Glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides

Glucose‐6‐Phosphate Dehydrogenases

“…The binding of NAD+, NADP', and NADPH to L. mesenteroides G6PD was measured using fluorescence techniques (143). The K,'s determined for NADP' (3 N) and NADPH (24 pM) were in reasonable agreement with the kinetically determined Ki values (282) of 5 and 37.6 pM, respectively, and for NADP', KD and Ki agreed with the K , of 5.7 pM (282).…”

“…For NAD' a large difference was noted between the KD determined by fluorescence techniques (2.5-2.8 mM) and the K, of 0.106 mM (282). Grove et al found that the glucose-6-P-competitive inhibitor glucose-1 -P lowered KD for NAD', suggesting that glucose-6-P may promote NAD' binding during catalysis (143).…”

“…Various analogs containing portions of the coenzyme structure were found to be coenzyme-competitive inhibitors for the G6PDs from human erythrocytes (97) and L. mesenteroides (143). Both these studies indicate that the adenosine-diphosphate moiety is more important than the nicotinamide portion for coenzyme binding, and that the 2'-phosphate on 2',5'-ADP and NADP' plays an especially important role in binding these ligands.…”

“…Both these studies indicate that the adenosine-diphosphate moiety is more important than the nicotinamide portion for coenzyme binding, and that the 2'-phosphate on 2',5'-ADP and NADP' plays an especially important role in binding these ligands. Kinetic studies (385a) using pairs of coenzyme analogs resembling the adenosine and nicotinamide portions of the coenzyme, respectively, revealed that no two coenzyme analogs could be accommodated simultaneously on the coenzyme binding site (143). Also, whereas NAD' quenched the protein fluorescence of L. mesenteroides GGPD, addition of nicotinamide mononucleotide plus ADP-ribose had no effect on enzyme fluorescence.…”

“…Also, whereas NAD' quenched the protein fluorescence of L. mesenteroides GGPD, addition of nicotinamide mononucleotide plus ADP-ribose had no effect on enzyme fluorescence. It was concluded that an intact coenzyme structure is necessary to accommodate both the nicotinamide and the adenosine portions of the coenzyme at its binding site on the enzyme (143). For the L. mesenteroides G6PD the dissociation constant of the E-NAD' complex is 3 orders of magnitude greater than the dissociation constant of E'-NADP' (143) (see Section IV.D.2), yet V,,, for the NADlinked reaction is 1.8 times as great as when NADP' is the coenzyme (Table VII).…”