Abstract
The oxidation of pharmacological amines such as histamine, 5-hydroxytryptamine and catecholamines is catalyzed by amine oxidizing enzymes from various origins (1, 2). These enzymes were classified into monoamine oxidase (2-5) and diamine oxidase (1, 6-10) according to their substrate specificity and susceptibility to inhibitors such as iproniazid and isoniazid. However, purified enzyme preparations were recently obtained from bovine plasma (11, 12), hog plasma (13) and pea seedlings (14, 15). They all have been often designated as amine oxidase, apart from the conventional classification, since these enzymes show properties of monoamine oxidase in their substrate specificity, and often behave also like diamine oxidase in substrate specificity and inhibition by isoniazid. It has been generally accepted that amine oxidases from various origins can take only molecular oxygen as hydrogen acceptor (1, 6, 16). However, there still remain many unsolved problems about the mechanism of electron transport to the acceptors via amine oxidases. The present paper reports evidences for the occurrance of transport of electron from histamine and some other amines to cytochrome c via diamine oxidase prepared from hog kidney or crystalline amine oxidase from Aspergillus niger. The latter enzyme was recently isolated by Yamada et al. (17) and was known to have the substrate specificity and susceptibility to inhibitors like diamine oxidase from hog kidney (18, 19). A preliminary report on these findings has been published earlier (32).
