Phospholipid Biosynthesis in Myelin: Presence of CTP: Phosphoethanolamine Cytidylyltransferase in Purified Myelin of Rat Brain

Publisher Website
Google Scholar
Abstract
Highly purified myelin from rat brain contains the ethanolaminephosphotranferase which completes the synthesis of phosphatidyl ethanolamine. Evidence was obtained for the presence in myelin of CTP:phosphoethanolamine cytidylyltransferase, the enzyme catalyzing formation of CDP-ethanolamine. Myelin was isolated by 2 different procedures, one based on the Norton-Poduslo method and the other involving repetitive gradients with osmotic shocking deferred to the end. Activity remained constant through all but the earliest steps suggesting the enzyme is intrinsic to myelin. Comparison of subcellular fractions revealed that .apprx. 1/2 the total activity was in the supernatant, the remainder being distributed among the particulate fractions. Relative specific activity of myelin was 27-31% that of microsomes, thus eliminating the possibility of appreciable contamination by the latter. The possibility of adsorption of the soluble enzyme by myelin was rendered unlikely by retention of activity after washing the myelin with buffered NaCl or sodium taurocholate. Relative specific activity of the cytidylytransferase was 10-fold higher than that of lactate dehydrogenase (a cytosolic marker) in myelin. The apparent Km for CTP was approximately the same for myelin and microsomes, but that for phosphoethanolamine was significantly higher for myelin.