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The oxidation of methionine by hydrogen peroxide, and the influence of iodide, pH, amino acids and selenite were studied with free methionine and with casein and fish fillet protein. The concentration levels tested ranged from 0·05 mm to 3·0 mm. Hydrogen peroxide oxidation was not influenced by pH in the range 5·0 to 8·0; at pH 8·5 the rate of oxidation was increased. When iodide was added in amounts equivalent to or less than the amounts of H2O2, the reaction was accelerated with free but not protein-bound methionine. At higher levels iodide inhibited the oxidation. An amino acid mixture and proteins inhibited the effect of iodide; this effect seemed to be due to tryptophan. Selenite also accelerated the effect of H2O2, both with free and with protein-bound methionine. Cu++ catalysed the oxidation by H2O2 at low reactant concentration but not at the higher levels. The reaction between methionine and H2O2 seemed to be of first order with respect to both reactants. 相似文献
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