Role of catalase in the oxidation of mercury vapor

Abstract

In human red blood cells the slow rate of production of hydrogen peroxide limits the rate of oxidation of mercury vapor. When H 2O 2 was added to blood samples, the rate of mercury uptake increased six times, but the inhibitory effect of KCN was less pronounced than in samples without H 2O 2, possibly because H 2O 2 tends to destroy cyanide. Only in the absence of exogenous H 2O 2 did the inhibition of oxidation of mercury vapor by different concentrations of KCN parallel the inhibition of catalase. Addition of peroxide to liver homogenates was without effect. When 20% (w/v) liver homogenates were exposed to mercury vapor at 37°, neither acatalasemia in mice nor pretreatment of rats with 2 g/kg of aminotriazole produced an appreciable decrease in the uptake of mercury during the 90-min incubation period. However, it was clear that catalase was responsible for the oxidation of mercury from the correlation ( r 2 = 0.85) between catalase activity and mercury uptake when 0.4 mg liver in 2 ml of incubation medium was exposed to mercury vapor. With higher concentrations of homogenates the availability of mercury limited the oxidation process. Experiments with horseradish peroxidase, beef liver catalase and inorganic catalysts of H 2O 2 decomposition indicate that the elemental mercury atom serves as an electron donor for complex I of catalase which is formed from the first reaction of catalase with H 2O 2. Other possible pathways of oxidation such as oxidation of elemental mercury by nascent oxygen released from H 2O 2 do not appear to be important.