Hydrogen peroxide steady state levels of 5 micromolar were determined in soybean (Glycine max) embryonic axes incubated for 2 hours and in axes pretreated with aminotriazole or cyanide, where these levels were 50 and 1 micromolar, respectively. The activities of catalase (105 picomoles H2O2 per minute per axis), peroxidase (10-44 picomoles H2O2 per minute per axis), glutathione peroxidase (3 picomoles H2O2 per minute per axis) and superoxide dismutase (3.5 units per axis), were also determined. Catalase seems to be the most important H2O2 consuming enzyme at the physiological concentration of H2O2. A short treatment with aminotriazole, while substantially increasing H2O2 level, did not affect the growth of the axes. The production of superoxide anion by the mitochondria isolated from soybean axes was measured from the superoxide dismutase-sensitive rate of adrenochrome formation in the presence of NADH or succinate as substrate and amounted to 1.3 and 0.8 nanomole O2− per minute per milligram protein, respectively. According to the stoichiometry of O2− and H2O2 dismutation reactions, it is apparent that about 0.9 to 1.5% of the total oxygen uptake proceeds through the formation of the free intermediates of the partial reduction of oxygen.
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