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Abstract
Abstract 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.
Highlights
Treatment of rat liver supernatant fractions with acetone and butanol to remove phospholipids resulted in very low transferase activity which could be increased up to 25-fold by the addition of suitable phospholipid preparations
Purified egg lecithin and lysolecithin, plant phophatidylethanolamine, and Adsorbosil for thin layer chromatog raphy were obtained from Applied Sciences Labs
A sample of egg lecithin supplied by Worthington was used in some experiments
Summary
Phosphorylcholine-methyl-14C was the product prepared enzymatically by rat liver supernatant fraction from choline chloride-methyl-' 4C and ATP as previously described [4]. CTP3H was prepared enzymatically by a rat liver cytoplasmic fraction as described by Hurlbert [5]. A sample of egg lecithin supplied by Worthington was used in some experiments. This sample was amber-colored and was found to be a mixture of several components on thin layer chromatogram& The lyso- derivatives of lecithin and phosphatidylethanolamine were prepared from the Applied Science Labs samples by the method of Long and Penny [6] with Crotalus adamanteusvenom (Ross Allen's Reptile Institute) as a source of phospholipase A
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