The biosynthesis of betaine and related compounds in higher plants and fungi

Abstract

A satisfactory synthesis of crystalline betaine aldehyde was achieved and methods were developed for the isolation and characterization of choline, betaine aldehyde, betaine and related compounds. The suitability of these methods (ion-exchange column chromatography and thin-layer chromatography in particular) were demonstrated by their application to the choline oxidase system known to exist in the mitochondria of rat liver. Attempts were made to demonstrate a similar choline oxidase system in plants. Experiments designed to demonstrate the existence of these enzymes by spectrophotometric and polarographic methods in mitochondria extracted from plant sources were largely unsuccessful. The mitochondria were structurally intact and were of high bio chemical integrity. On the isolated occasions when stimulation of respiration occurred when choline was supplied as substrate, the formation of betaine aldehyde or betaine was never confirmed by the characterization techniques which had been developed. The existence of a permeability barrier to the uptake of choline was discounted as an explanation of the 'latency' of the enzymes investigated. The methods employed to overcome such a barrier in mitochondria extracted from rat liver were without effect on the plant systems. Radioactive choline was taken up by mitochondria, from plants and a fraction of the labelled compound became closely associated with the mitochondrial membranes. However, the level of radioactivity did not increase with time indicating an upper limit of choline uptake or a continual utilization of the choline taken up. The existence of an alternative pathway for the oxidation of choline was superficially examined but no definite conclusions could be reached.