Histochemical Localization of Choline Oxidase in Rat Liver and Kidney

Abstract

RAT liver is capable of oxidizing hydrolysed acetylcholine¹. It was shown to be due to oxidation of choline, and betaine aldehyde is the oxidation product². The oxidase system involved was found to consist of a dehydrogenase, choline dehydrogenase, cytochrome C and cytochrome oxidase³. Though this enzyme system does not need diphosphopyridine nucleotide (DPN), yet it is sensitive to the action of amytal⁴. This oxidase system is also sensitive to antimycin A, cyanide and azide, but to a much lesser extent than that of succinic oxidase system⁵. These findings indicate that a respiratory chain identical to that of succinic oxidase may be involved in the hydrogen transfer from choline. According to some authors, flavin adenine dinucleotide (FAD) may be involved in this reaction⁶, but by others it plays no part at all⁷. Choline oxidase activity was studied biochemically using different hydrogen acceptors as ferricyanide, methylene blue, cytochrome C, 2,6-dichlorophenol indophenol⁸ and triphenyl tetrazolium bromide⁹. But phenazine methosulphate was found to be the only reliable hydrogen acceptor for purified choline dehydrogenase⁷. This oxidase may play an important part in the transfer of labile methyl group to methionine¹⁰.