Metabolic studies of N-bases of phospholipids and long chain bases of sphingolipids in two-weeks-old mouse brain tissue in comparison with one-month-old mouse visceral tissues.

After intraperitoneal administration of 15N-labeled serine, ethanolamine and choline to young mice showing active myelination, the incorporation of 15N-atom into N-bases of phospholipids and long chain bases of sphingolipids in brain tissue was particularly investigated in comparison with those in visceral tissues of adult mouse. After intraperitoneal injection of DL-[15N]-serine into mice, it was found that the 15N-atom was obviously incorporated into phosphatidylserine, phosphatidylethanolamine, ethanolamine-plasmalogen and long chain bases of cerebroside, sphingomyelin and gangliosides, but not significantly into phosphatidylcholine. The apparent maximum rates of the incorporation were also calculated. After administration of [15N]-ethanolamine, the 15N-atom was predominantly incorporated into phosphatidylethanolamine and next into ethanolamine-plasmalogen, but also not significantly into phosphatidylcholine. After administration of [15N]-choline chloride, the 15N-atom was incorporated into phosphatidylcholine and sphingomyelin, but not into other phospholipids and sphingolipids. These results suggested that serine, ethanolamine and choline are available for the biosynthesis of the N-bases of phospholipids in the brain tissue of young mouse and that serine is also utilized for the biosynthesis of long chain bases of sphingolipids. However, neither biosynthesis of choline from ethanolamine nor of phosphatidylcholine from phosphatidylethanolamine by methylation seemed to take place even in the brain tissue of young mouse, while the decarboxylation of phosphatidylserine into phosphatidylethanolamine was obviously observed. The decarboxylation rate of phosphatidylserine into phosphatidylethanolamine in the brain tissue of young mouse seemed to be approximately at the same level with the other tissues like liver, lung spleen and kidney of adult mouse.