Phosphatidylcholine phosphoglyceride synthesis

Phosphatidate is formed by successive acylations of glycerol 3-phosphate by acyl Co A. Flydrolysis of its phosphoryl group followed by acylation yields a triacylglycerol. CDP-diacylglycerol, the activated intermediate in the de novo synthesis of several phospholipids, is formed from phosphatidate and CTP. The activated phosphatidyl unit is then transferred to the hydroxyl group of a polar alcohol, such as inositol, to form a phospholipid such as phosphatidylinositol. In mammals, phosphatidylethanolamine is formed by CDP-ethanolamine and diacylglycerol. Phosphatidylethanolamine is methylated by S-adenosylmethionine to form phosphatidylcholine. In mammals, this phosphoglyceride can also be synthesized by a pathway that utilizes dietary choline. CDP-choline is the activated intermediate in this route. 

Phospholipid concentrations vary from 0.2 to 14 mg P/kg soil (Kowalenko and Mc-Kercher, 1971a). These represent between 0.5% and 7% of the soil organic phosphorus, with an average of 1% (Anderson and Malcolm, 1974). The soil phospholipids may be of microbial, plant or animal origin. Their synthesis and degradation in soil may be quite rapid. Phosphoglycerides (phosphatidylcholine, phosphatidylethanol-amine) seem to be prevalent and may represent up to 40% of the phospholipids (Dalai, 1977). 

Lipotropic substances compounds directly or indirectly involved in fat metabolism, which can prevent or correct fatty degeneration of the liver. They serve as substrates of phosphatide biosynthesis, or contribute (e.g. by methylation) to the synthesis of these substrates. Thus choline and any substance capable of contributing methyl groups for choline synthesis (e.g. methionine) are L.s. Liver is the major site of synthesis of plasma phosphoglycerides when the availability of choline is restricted, the rate of phosphatidylcholine synthesis decreases, and the rate of removal of fatty acids from the liver falls below normal. If the rate of supply of fatty acids (free and esterified) to the liver remains normal, the resulting accumulation of fat gives rise to the condition of fatty liver, or fatty degeneration of the liver. 

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