INDOLYLPROPIONIC ACID OXIDATION BY PEROXIDASE 359 SUMMARY 1. The oxidation of IPA and IBA by oxygen is catalysed by highly purified horseradish peroxidase preparations in the presence of Mn2+. 2. The mechanism of the reaction has not been elucidated but the formation of hydrogen peroxide as an obligatory intermediate is suggested by the inhibiting effect of catalase. 3. It is suggested that the previously reported oxidation of IPA and IBA by plant extracts may have been due to the presence of peroxidase and Mn2+ in the extracts.

The chemical fate of methyl bromide absorbed by wheat under the conditions of fumigation has been studied. Whole-wheat flour was exposed to 14C-labelled methyl bromide. The fat, starch, gluten, and water-soluble fractions were prepared from the exposed flour and their I4C-content assayed. The gluten or protein fraction was responsible for some 8004 of the decomposition of the absorbed fumigant. By measuring the 14C of the volatile products obtained on treating the gluten with sodium hydroxide or hydriodic acid under different conditions, it was shown that the decomposition of methyl bromide in gluten was due almost entirely to methylation with the formation of 50% of N-methyl derivatives, 30% of dimethyl sulphonium derivatives, and of 20% of methoxyl and thiomethoxyl derivatives in about equal proportions. Similar results were obtained when gluten alone was exposed to the labelled fumigant. The production of free methanol in the flour by hydrolysis of the absorbed fumigant was about 10% or less. The rate of spontaneous decomposition of the dimethyl sulphonium compounds formed as a result of fumigation was estimated by using wheat which had been grown on 35S-labelled sulphate.'

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