Mercury Vapor Uptake and Oxidoreductases in Erythrocytes

Abstract

The inhibition by ethanol of the absorption of inhaled Hg^o suggested the participation of catalase in this process (Nielsen-Kudsk, 1969). The studies reported there specified the mechanisms by which H2O2-metabolizing enzymes in erythrocytes enhance or reduce the accumulation of Hg after exposure to Hg^o.

When red-blood-cell suspensions were exposed to Hg_o in a closed system, it was found that the mercury was absorbed by the cells only. Thus, a low hematocrit led to a high cellular Hg uptake, alterations of which could therefore be analyzed easier. The uptake was inducible by slow infusion of small amounts of H₂O₂ and paralleled the activity of catalase as was shown by selecting red cells from species with largely different H2O2-metabolizing enzyme activities. The instrumental function of the catalase- H₂O₂ intermediate (compound-I) in Hg uptake was further verified by its sensitivity to ethanol or aminotriazole (AT).

The essentiality of H₂O₂ as a cofactor strongly suggested a modulation of Hg uptake by glutathione and its peroxidase (GSH/GSH-Px). GSH-dependent H₂O₂ removal was inactivated by conjugation of GSH to chlorodinitrobenzole or by t-butylhydroperoxide (t-BOOH) as substrate for GSH-Px. Both treatments significantly enhanced that uptake which could be stimulated by exogenous H₂O₂. Yet the presence of t-BOOH strongly augmented the Hg uptake even without added H₂O₂. As this augmentation was sensitive to AT, it probably resulted from compound-I formed by endogenous H₂O₂ production.

The experiments made evident that elemental Hg is oxidized by a peroxidatic reaction with catalase, a process which is enhanced by the inactivation of the GSH/GSH-Px system.