Mechanisms of Protection of Catalase by NADPH

Abstract

NADPH is known to be tightly bound to mammalian catalase and to offset the ability of the substrate of catalase (H 2 O 2 ) to convert the enzyme to an inactive state (compound II). In the process, the bound NADPH becomes NADP ؉ and is replaced by another molecule of NADPH. This protection is believed to occur through electron tunneling between NADPH on the surface of the catalase and the heme group within the enzyme. The present study provided additional support for the concept of an intermediate state of catalase, through which NADPH serves to prevent the formation (rather than increase the removal) of compound II. In contrast, the superoxide radical seemed to bypass the intermediate state since NADPH had very little ability to prevent the superoxide radical from converting catalase to compound II. Moreover, the rate of NADPH oxidation was several times the rate of compound II formation (in the absence of NADPH) under a variety of conditions. Very little NADPH oxidation occurred when NADPH was exposed to catalase, H 2 O 2 , or the superoxide radical separately. That the ratio exceeds 1 suggests that NADPH may protect catalase from oxidative damage through actions broader than merely preventing the formation of compound II.

Model of 2,3-bisphosphoglycerate metabolism in the human erythrocyte based on detailed enzyme kinetic equations: equations and parameter refinement

“…Thus, under these conditions the simple model of ' ATPase ' may have been inadequate. However, at a Glc(1,6)P # concentration approximately double the normal value, the model predicted a glycolytic rate of 1.13 mmol:litre of erythrocytes −" :h −" with or without the assumption of constant ATP concentration, while Piatti et al [20] measured a value of 1.06p0.10 mmol:litre of erythrocytes −" :h −"…”

“…Piatti et al [20] overloaded human erythroyctes with Glc(1,6)P # to investigate possible regulatory roles of it in i o ; they reported that, when erythrocytes are overloaded with about five times the normal concentration of Glc(1,6)P # , the glycolytic rate falls from 1.42p0.15 to 0.71p0.08 mmol:litre of erythrocytes −" : h −" , the concentrations of glucose 6-phosphate (Glc6P) and fructose 6-phosphate (Fru6P) fall by $ 50 %, and the concentration of ATP remains approximately constant. It was only possible to obtain a good match between these findings and the output of the model if it was assumed that PFK is weakly activated by Glc(1,6)P # .…”

“…However, when the kinetic parameters reported for 6-PGDH were incorporated into the complete metabolic model, simulations of the in i o steady-state gave concentrations of 6-PG of $ 0.3 mM ; 6-PG is usually present in about micromolar concentrations [20]. In order to increase the activity of 6-PGDH, and hence lower the simulated in i o steady-state concentration of 6- [87] showed that the allosteric and co-operative properties of PK are strongly influenced by pH and this suggested that the transition from R to T involves a deprotonation ; examination of the values that these workers obtained for L at different pH values shows that they are most closely matched if it is assumed that n l 1 (to the nearest integer) ; the pH-dependence of the inhibition of erythrocyte PK by iodoacetamide involves a group that has a pK a of 6.8 [88] ; it was assumed that this was the group that was involved in the R-to-T transition.…”

“…(4) Many important pH effects, as well as potentially important glycolytic effectors, such as glucose 1,6-bisphosphate [Glc (1,6)P # ] [19,20], have been neglected.…”

Asparagus racemosus extract increases the life span in Drosophila melanogaster

“…Glutathione reductase requires NADPH to regenerate reduced glutathione [51]. Catalase converts hydrogen peroxide to less toxic compounds in the presence of NADPH [52,53]. Hence the major antioxidant systems are dependent on the availability of NADPH that is principally produced by G 6 PD.…”