Cxxxviii. Hepatic Oxidation of Choline and Arsenocholine

IT was shown by Mann & Quastel [1937] that choline is oxidized by slices or extracts of rat liver and kidney. The oxidation product was isolated and identified as betaine aldehyde. Some evidence was obtained that betaine aldehyde is also oxidized by the same tissues though at a much slower rate than choline and it was suggested that the oxidation product in this case is betaine. Bernheim & Bernheim [1933] observed an increase in oxygen uptake when acetylcholine was added to extracts of liver and kidney of rat and cat and suggested that it was due to choline oxidation. The same authors in 1938 [cf. also Bernheim & Webster, 1937] arrived at the conclusion that betaine aldehyde is formed, without, however, isolating it. They showed that synthetic betaine aldehyde is oxidized by liver extract, the rate of oxidation being dependent upon pH. At pH 7x8 it is oxidized presumably to betaine but at pH 6-7 the aldehyde suffers little change. In the present work it is shown that one of the components of the cholineoxidizing system is a typical dehydrogenase which can bring about the oxidation of choline anaerobically, provided that a suitable hydrogen acceptor is present, and which is insensitive to low concentrations of cyanide though the complete system is cyanide-sensitive. Some evidence is also put forward which indicates that the other components of the oxidizing system are cytochrome and indophenol oxidase. The oxidation of arsenocholine by the same system is also described. Methods