Effect of pyridoxine deficiency on phospholipid methylation in rat liver microsomes

The effect of altered methionine metabolism during pyridoxine deficiency on the activity of phosphatidyl-ethanolamine methyltransferase (EC 2.1.1.17) and the levels of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) has been evaluated in rat liver microsomes. Animals fed a pyridoxine-deficient diet for 7 wk displayed a fivefold increase in the hepatic tissue level of S-adenosylhomocysteine when compared to either control or pair-fed animal counterparts. When PE methyltransferase was assayed in vitro, a significant increase in specific activity was observed using enzyme preparations from either pair-fed or pyridoxine-deficient rats. On the other hand, phospholipid levels did not conform to the measured enzyme activity. The level of PC in microsomes from either pyridoxine-deficient or pair-fed animal groups was significantly lower than that determined for the control group of rodents. However, the level of PC was noticeably lower in microsomes from pyridoxine-deficient animals than that from pair-fed animals, which received 45% of the feed intake of the control animals. In addition, the level of PE in microsomes from pair-fed and pyridoxine-deficient animals was significantly higher than that analyzed from the control animals, further confirming decreased methylation of substrate to product. It is concluded that pyridoxine deficiency may alter the methylation of phospholipid in the endoplasmic reticulum above and beyond that produced by feed restriction alone.