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Journal of Lipid Research, Vol. 11, 544-550, November 1970
Copyright © 1970 by Lipid Research, Inc.

Biosynthesis of retinal phospholipids: incorporation of radioactivity from labeled phosphorylcholine and cytidine diphosphate choline

J. G. Swartz and J. E. Mitchell

Department of Ophthalmology, The Mount Sinai School of Medicine, New York 10029

Phosphorylcholine-1,2-¹⁴C and choline-1,2-¹⁴C-labeled cytidine diphosphate choline are incorporated into lecithin by whole homogenates and particulate fractions of rat retina with optimal incorporation of label by the microsomal fraction. The soluble fraction contains a factor(s) which stimulates incorporation of label with release of inorganic phosphate. Mg⁺⁺ is required for optimal incorporation of intermediates into lecithin in the presence of added diglycerides; without added diglycerides, incorporation of phosphorylcholine or cytidine diphosphate choline was moderately stimulated by preincubating the system in the absence of Mg⁺⁺ with added phosphatidic acid and by adding this mixture to fresh enzyme and the complete incubation mixture (including Mg⁺⁺). The results show that the retina is capable of de novo synthesis of phosphatides and suggest that the rod outer segments depend on the pigment epithelium and(or) the inner rod segments for a source of phospholipids. Coenzyme A and ATP added to whole homogenate of retina did not significantly increase the incorporation of CDP-choline-1,2-¹⁴C into lecithin but slightly increased the radioactivity found in lysolecithin and sphingomyelin. Rats with hereditary retinitis pigmentosa have an abnormally high lipid phosphorus content of the retina, but they do not incorporate labeled CDP-choline into lecithin of retina at a higher rate than do normal animals.

Supplementary key words cytidyl transferase • glyceride transferase • retinitis pigmentosa

Submitted on August 6, 1969
Revised on June 30, 1970
Accepted on July 31, 1970

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