Lecithin biosynthesis in the rat studied with phosphonate analogues of phosphorylcholine

Abstract

1.1. Lecithin biosynthesis has been studied by comparing the incorporation into rat phospholipids of phosphorylcholine and some of its phosphonate analogues, namely 2-trimethylaminoethylphosphonic acid and 3-trimethylaminopropylphosphonic acid.2.2. The P-C bond of neither analogue was broken in the rat. There were no signs of any demethylation taking place.3.3. 2-Trimethylaminoethyl -and 3-trimethylaminopropylphosphonic acids were incorporated in vivo into rat liver and kidney phospholipids as a unit. The only radioactive lipids formed were the phosphonate analogues of lecithin.4.4. The results indicate that the phosphonate analogues are incorporated into phosphonolecithins by the same mechanism as phosphorylcholine into lecithin, the CMP derivatives being intermediates in the reaction. A partly purified cytidylyl-transferase (EC 2.7.7.15) incorporated 2-trimethylaminoethylphosphonic acid into the CMP derivative. Phosphorylcholine behaved as a strong competitive inhibitor of the reaction.5.5. The distribution of radioactivity within different phosphonolecithin sub-species after in vivo labelling with 3-trimethylaminopropylphosphonic acid was very similar to the radioactivity distribution within lecithin subspecies after choline labelling.6.6. The results suggest that most of the choline incorporation into lecithin in vivo occurs by the same mechanism as phosphorylcholine.