Occurrence and Biosynthesis of Ceramide Phosphorylethanolamine in Chicken and Rat Liver

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Abstract
Ceramide phosphorylethanolamine has been found to occur in chicken and rat liver. An enzyme (CDP-ethanolamine:ceramide ethanolaminephosphotransferase) has been found in a number of tissues which catalyzes the biosynthesis of this lipid. The enzyme catalyzes the transfer of the phosphorylethanolamine moiety of CDP-ethanolamine to the free primary hydroxyl group of a ceramide (N-acylsphingosine). The chicken liver enzyme requires 0.010 M manganese ions for optimal activity and has a pH optimum of 7.7. The Km for the substrate N-octanoyl-threo-sphingosine was found to be 2.5 × 10−4 M. A study of the effect of increasing CDP-ethanolamine concentration on the reaction rate indicates from sigmoid kinetics that the coenzyme modulates and possibly regulates PE-ceramide transferase activity. The enzyme differs from sphingomyelin synthetase (CDP-choline:ceramide cholinephosphotransferase) in that it will only utilize the unnatural threo isomer of N-acylsphingosines (threo-ceramides) as acceptors for the phosphorylethanolamine moiety of CDP-ethanolamine. Sphingomyelin synthetase has been shown to utilize erythro-ceramides the presence of sulfhydryl reagents (Sribney, M.: Can. J. Biochem. 49, 306 (1971)); the enzyme catalyzing the biosynthesis of ceramide phosphorylethanolamine, however, does not do so, even in the presence of a variety of sulfhydryl reagents tested.

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