Divalent cation dependent ATPase activities of red blood cell membranes: influence of the oxidation of membrane thiol groups close to each other

Inhibition of membrane erythrocyte (Ca2+ + Mg2+)-ATPase by hemin

Red blood cell lysis is a common symptom following severe or prolonged oxidative stress. Oxidative processes occur commonly in sickle cells, probably mediated through denatured hemoglobin and the accumulation of ferric hemes in the membranes. Calmodulin-stimulated (Ca2+ + Mg2+)-ATPase from sickle red cell membranes is partially inactivated (Leclerc et al. (1987) Biochim. Biophys. Acta 897, 33-40). In this study (Ca2+ + Mg2+)-ATPase activity from normal adult erythrocyte membranes was measured in the presence of hemin. We report a time- and concentration-dependent inhibition of the activity of the enzyme by hemin due to a decrease in the maximum velocity. Only a mild inhibitory effect was observed in the presence of iron-free protoporphyrin IX, indicating the catalytic influence of the iron. Experiments carried out with hemin (ferric iron) liganded with imidazole or with reduced protoheme (ferrous iron) liganded with carbon monoxide, demonstrated that the inhibition requires that hemin be capable of binding additional ligands. The inhibition was not influenced by the absence of oxygen but was prevented by addition of bovine serum albumin. Addition of butylated hydroxytoluene, a protective agent of lipid peroxidation, failed to prevent the inhibition of calmodulin-stimulated (Ca2+ + Mg2+)-ATPase. As dithiothreitol partially restores the enzyme activity, we postulated that hemin interacts with the thiol groups of the enzyme.

The calmodulin-stimulated (Ca2+ + Mg2+)-ATPase in hemoglobin S erythrocyte membranes: effects of sickling and oxidative agents

A decrease in the reactivity of erythrocyte membrane (Ca2+ + Mg2+)-ATPase to calmodulin stimulation has been observed in aging red cells and in various types of hemolytic anemias, particularly in sickle red cell membranes. Unlike the aging process, the defect in the (Ca2+ + Mg2+)-ATPase from SS red blood cells is not secondary to a decrease in calmodulin activity and is already present in the least dense SS red blood cells separated on a discontinuous density gradient. Deoxygenated AS red cells were forced to sickle by lowering the pH, raising the osmolarity of the buffer (sickling pulse). Under these conditions an inhibition of the calmodulin-stimulated enzyme was observed only if several cycles of oxygenation/deoxygenation were applied. No alteration of the enzyme could be detected after submitting AS red blood cells to other conditions or in AA red blood cells submitted to the same treatments. This suggests that oxidative processes are involved in the alterations of the (Ca2+ + Mg2+)-ATPase activity. Treatment of membranes from AA erythrocytes by thiol group reagents and malondialdehyde, a by-product of auto-oxidation of membrane unsaturated lipids and a cross-linking agent of cytoskeletal proteins, led to a partial inhibition of the calmodulin-stimulated (Ca2+ + Mg2+)-ATPase. We postulate that the hyperproduction of free radicals described in the SS red blood cells and involved in the destabilization of the membrane may be also responsible for the (Ca2+ + Mg2+)-ATPase failure.

Inhibition of erythrocyte Ca2+-ATPase by activated oxygen through thiol- and lipid-dependent mechanisms

We have studied erythrocyte Ca2+-ATPase as a model target for elucidating effects of activated oxygen on the erythrocyte membrane. Either intracellular or extracellular generation of activated oxygen causes parallel decrements in Ca2+-ATPase activity and cytoplasmic GSH, oxidation of membrane protein thiols, and lipid peroxidation. Subsequent incubation with either dithiothreitol or glucose allows only partial recovery of Ca2+-ATPase, indicating both reversible and irreversible components which are modeled herein using diamide and t-butyl hydroperoxide. The reversible component reflects thiol oxidation, and its recovery depends upon GSH restoration. The irreversible component is largely due to lipid peroxidation, which appears to act through mechanisms involving neither malondialdehyde nor secondary thiol oxidation. However, some portion of the irreversible component could also reflect oxidation of thiols which are inaccessible for reduction by GSH, since we demonstrate existence of different classes of thiols relevant to Ca2+-ATPase activity. Activated oxygen has an exaggerated effect on Ca2+-ATPase of GSH-depleted cells. Sickle erythrocytes treated with dithiothreitol show a heterogeneous response of Ca2+-ATPase activity. These findings are potentially relevant to oxidant-induced hemolysis. They also may be pertinent to oxidative alteration of functional or structural membrane components in general, since many components share with Ca2+-ATPase both free thiols and close proximity to unsaturated lipid.

Redox status and pulmonary vascular reactivity

Oxygen radicals are produced during oxidative metabolism in proportion to the tissue oxygen tension. The studies reported here have shown that oxygen radicals or the sulfhydryl oxidant, diamide, caused pulmonary vasodilatation in the isolated perfused rat lung. Could oxygen radicals play a role in the physiologic control of pulmonary vascular smooth muscle tone?

Phosphorylated intermediates of two Ca++-ATPases in membrane preparations from lens epithelial cells

By incubating preparations enriched in membranes from lens epithelial cells with [gamma 32P]-ATP and Ca++ at 0 degrees C for 15 seconds followed by SDS-PAGE analysis, it was possible to demonstrate a Ca++-dependent [32P]-phosphate incorporation in two polypeptides with Mr 105,000 and 140,000. Treatment of phosphorylated preparations with 0.06 N hydroxylamine at pH 5.4 and 25 degrees C removed the label from both polypeptides indicating that the phosphate was attached to the proteins by an anhydride linkage characteristic of the phosphorylated intermediates of the ATPases. Membrane preparations from sarcoplasmic reticulum and red blood cell studied under the same conditions showed a Ca++-dependent [32P]-phosphate incorporation into polypeptides with Mr 105,000 and 138,000, respectively, corresponding to the phosphorylated intermediates of the Ca++-ATPases present in these preparations. The results suggest the presence of two Ca++-ATPases in lens epithelial cells which, in terms of Mr, appear to be similar to those present in the sarcoplasmic reticulum and the red blood cell plasma membrane, respectively.

Erythrocyte (Ca+2 + Mg+2)-ATPase activity: increased sensitivity to oxidative stress in glucose-6-phosphate dehydrogenase deficiency

The effect of the thiol-oxidizing agent diamide on erythrocyte (Ca+2 + Mg+2)-ATPase activity was measured in normal and glucose-6-phosphate-dehydrogenase-deficient (G6PD-) cells. Although the enzyme activity before the oxidative stress was similar in both groups, diamide induced a markedly greater inhibition in the enzyme activity in the G6PD- cells than in the normal controls. These data indicate dependence of erythrocyte (Ca+2 + Mg+2)-ATPase, in part, on the redox status of the cell. The increased vulnerability of (Ca+2 + Mg+2)-ATPase to oxidative stress in G6PD- may be of pathophysiological relevance to their premature destruction in oxidant-induced hemolysis.

Membrane thiol-disulfide status in glucose-6-phosphate dehydrogenase deficient red cells. Relationship to cellular glutathione

The behavior of glucose-6-phosphate dehydrogenase (G6PD)-deficient red cell membrane proteins upon treatment with diamide, the thiol-oxidizing agent (Kosower, N.S. et al. (1969) Biochem. Biophys. Res. Commun. 37, 593-596), was studied with the aid of monobromobimane, a fluorescent labeling agent (Kosower, N.S., Kosower, E.M., Newton, G.L. and Ranney, H.M. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 3382-3386) convenient for following membrane thiol group status. In diamide-treated G6PD-deficient red cells (and in glucose deprived normal cells), glutathione (GSH) is oxidized to glutathione disulfide (GSSG). When cellular GSH is absent, membrane protein thiols are oxidized with the formation of intrachain and interchain disulfides. Differences in sensitivity to oxidation are found among membrane thiols. In diamide-treated normal red cells, GSH is regenerated in the presence of glucose and membrane disulfides reduced. In G6PD-deficient cells, GSSG is not reduced, and the oxidative damage (disulfide formation) in the membrane not repaired. Reduction of membrane disulfides does occur after the addition of GSH to these membranes. A direct link between the thiol status of the cell membrane and cellular GSH is thereby established. GSH serves as a reductant of membrane protein disulfides, in addition to averting membrane thiol oxidation.

Sensitivity to radiations of Mg2+ and (Ca2+ + Mg2+) ATPase activities associated with erythrocyte membrane fragments

Treatment of disrupted erythrocyte membranes with ionizing radiation induces a partial oxidation of -SH groups (as expected from reported data) and a loss of membrane phospholipids as confirmed by the decrease of membrane amino groups. The resulting disturbance of the membrane assembly strongly affects the membrane bound divalent cation-dependent ATPase activities, possibly by causing the formation of a dead-end enzyme complex unable to complete the ATP splitting cycle.