Some Investigations on Choline Metabolism in Aspergillus niger

1. Chapter I gives a survey of the literature on the metabolism of choline in plants and animals. The synthesis of choline appears to progress via methylation of ethanolamine. The methylgroups required in animals are mainly supplied by compounds with biologically labile methylgroups present in the ration. The existence of the synthesis of methylgroups from compounds like formic acid is found only when special conditions prevail. In plants the methylgroups are synthesized from “one C-fragments”. The synthesized choline can be built in (lecithin); during dissimilation it can be converted into trimethylamine and into betaine. 2. Chapter II proceeds to describe the methods of determining total, free, lipoid and watersoluble bound choline and betaine. 3. Chapter III mentions the results of a comparative investigation on the determination of choline according to 2 different methods. By the determinations of the choline fractions in plants it appeared, that in the higher plant the amount of total choline consisted mainly of lecithin and in the lower plant mainly of watersoluble bound choline. Lecithinase C present in the higher plant might give a wrong impression of the constitution of the choline fractions. 4. Chapter IV describes the dissimilation of choline in Aspergillus niger: the fungus appeared to oxidise added choline to betaine; oxidation under anaerobic conditions is small in comparison to oxidation under aerobic conditions. No relation between the dissimilation of choline and the metabolism of carbohydrate could be found. 5. Chapter V mentions the investigation of the synthesis of choline in Aspergillus niger: In the presence of carbohydrates a synthesis of choline from methionine and ethanolamine takes place. We have tried to obtain more data on the relation between the metabolism of carbohydrates and the synthesis of choline; Cantoni’s supposition that the transfer of the methylgroup of methionine occurs by means of ATP is to be preferred to that of Barrenscheen, who supposes the transfer takes place after oxidation of methionine to methioninesulfoxide.