Biosynthesis of Phosphatidylcholine in Euglena gracilis*†

Abstract

SYNOPSIS. Extracts of Euglena gracilis carry out a very rapid but limited synthesis of phosphatidylcholine when S-adenosylmethionine or A T P and methionine are supplied. Cytidinediphosphocholine ap-HE biosynthesis of phosphatidylcholine (PC) has been T well characterized with respect to the nature of the precursors and intermediate compounds in higher animals. Two pathways are found in a variety of animal tissues: ( a ) phosphocholine is transferred from cytidinediphosphocholine to Il2-diglyceride to form PC and cytidylic acid( 1 8~9 ) ; ( b ) phosphatidylethanolamine (PE) is methylated in 3 successive reactions with S-adenosylmethionine as the methylgroup donor (3,4,5,7,8,10,12).Although most animal tissues have a greater capacity to synthesize PC by the CDP-choline pathway than by methylation of PE (4), it appears that all the choline produced in the animal body arises through methylation of PE (7); at any rate, no other means of synthesizing choline in animals is now known. The CDP-choline pathway apparently serves to conserve methyl groups in the animal body. Synthesis of PC from CDP-choline has not been shown to occur outside the animal kingdom.The methylation pathway has been clearly shown in Agrobacterium tumefaciens( 17), and there is good circumstantial evidence that it functions in the mold Neurospora crassa( 13). The photosynthetic protozoon Ochromonas malhamensis has been shown to produce lipid-bound C14labeled choline from C14-methionine( 20), again indicating operation of the methylation pathway. A . tumefaciens will utilize exogenous choline for lipid synthesis, but attempts to find enzymes of the CDP-choline pathway were unsuccessful (22). Choline is also utilized by Neurospora for phospholipid synthesis, but the enzymatic steps were not examined ( 1 1 ) .Phospholipid metabolism has been studied very little in plants and the photosynthetic protozoa. In the work described here, attempts were made to find PC synthesis in extracts of Euglena gracilis, using the substrates of both the CDP-choline pathway and the methylation pathway. MATERIALS AND METHODSCDP-choline, BSA and Tris buffer were obtained from Sigma Chemical Co., St. Louis, Mo. ; L-methionine hydrochloride, egg lecithin, and lipase (Steapsin) from Nutritional Biochemicals Corp., Cleveland, Ohio ; and (-) -S-adenosyl-L-methionine iodide (84.1%

Phospholipid biosynthesis in the anaerobic protozoon Entodinium caudatum

“…The failure to detect phosphatidylcholine after [2-14C]ethanolamine or [Me-14C]methionine labelling indicates that the organism cannot synthesize phosphatidylcholine by the donation ofmethyl groups from S-adenosylmethionine to phosphatidylethanolamine. This sharply contrasts with the situation in the tissues of higher animals and in many aerobic protozoa such as T. pyriformis (Smith & Law, 1970), Euglenagracilis (Tipton & Swords, 1966) and Ochromonas malhamensis (Lust & Daniel, 1966) in which the presence of a methylation pathway for phosphatidylcholine synthesis has been well established. However, E. caudatum is certainly not unique in this respect, as it has been reported that the methylation pathway does not exist in the parasitic proto-1975 zoon Plasmodium knowlesi (Rock, 1971) and in mammalian brain (Ansell, 1973).…”

The metabolism of rumen ciliate protozoa

“…In this respect Ent. caudatum therefore resembles Plasmodium knowlesi [81] and differs from Tetrahymena pyriformis [82] and Euglena gracilis [83], where methylation of ethanolamine is an important source of choline.…”