The Role of Phospholipids in Stimulating Phosphorylcholine Cytidyltransferase Activity

From the ¹ From the Laboratory of Biochemistry, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20014

The phosphorylcholine cytidyltransferase activity of fresh rat liver supernatant fractions was observed to be stimulated by boiled, previously incubated particulate fractions of rat liver. This stimulation was shown to be mediated by the phospholipids present in the latter.

Treatment of rat liver supernatant fractions with acetone and butanol to remove phospholipids resulted hi very low transferase activity which could be increased up to 25-fold by the addition of suitable phospholipid preparations.

Lipid extracts of fresh rat liver homogenates did not stimulate transferase activity unless they were exposed to a continuous flow of air for 15 hours leading to lipid oxidation. Fractionation of the phospholipids of fresh and incubated rat liver homogenates showed that lysophosphatides were present in higher concentrations in the latter and were the most active phospholipids in stimulating transferase activity. Similarly, highly purified egg lecithin showed little ability to stimulate transferase activity whereas egg lysolecithin was highly active. None of the individual isolated phospholipids stimulated to the same degree as unfractionated rat liver lipid preparations.

The stimulation of transferase activity by degraded phospholipids is suggested to represent a positive feedback mechanism for the control of phospholipid synthesis.

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