Abstract
Preliminary studies carried out in order to find the optimal conditions for the assay of diamine oxidase activity in rabbit liver homogenate, showed that the oxidation of the substrates histamine and cadaverine at alkaline pH (∼ 8.0) was not inhibited by aminoguanidine and hydroxylamine (specific inhibitors of diamine oxidase), but was blocked by octanol (specific inhibitor of monoamine oxidase) which was uneffective at lower pH values. Borate inhibited diamine oxidase but not monoamine oxidase activity, since its inhibitory effect, at different pH values, was very similar to that of aminoguanidine and hydroxylamine. Diamine oxidase from rabbit liver seemed to be active only at almost neutral pH values. At alkaline pH values, the oxidation of histamine and cadaverine was operated by monoamine oxidase. Furthermore cadaverine‐oxidizing activity, when assayed at pH 8.8, exhibited the same subcellular distribution as monoamine oxidase. When assayed at a pH near neutrality the bulk of diamine‐oxidizing activity (both with cadaverine and histamine as substrates) was present in the microsomal fraction.
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