No abstract

THERE have been a number of investigations on the incorporation of labelled lipid bases into tissue phospholipids in viva (e.g. ELWYN, WEISSBACH, HENRY and SPRINSON, 1955; BREMER, FIGARD and GREENBERG, 1960;NEMER and ELWYN, 1960;WISE and ELWYN, 1965; BJDRNSTAD and BREMER, 1966). These have usually followed the fate in tissues after intravenous or intraperitoneal injection of the base. In a few experiments the incorporation of a labelled base into brain lipids has been followed after such an injection. Thus, the labelling of a variety of lipids in the brain of the rabbit after the intraperitoneal injection of ~-[3-~~C]serine was investigated by DAVISON, MORGAN, WAJDA and PAYLING-WRIGHT (1 959), and also briefly described by ANSELL and SPANNER (1962a). GROTH, BAIN and PFEIFFER (1958) studied the fate of both 14C-labelled choline and 2-dimethylaminbethanol in brain and liver after intraperitoneal injection, though they did not investigate the lipid fractions into which the bases were incorporated. ANSELL and SPANNER (1962b) showed that 2-dimethylaminoethanol was phosphorylated in brain and Iiver and could be incorporated into a phospholipid.Fewer experiments have been carried out on the fate of intracerebrally injected bases though the fate of their [32P]phosphate esters was studied by KOMETIAM (1963) and ANSELL and CHOJNACKI (1963). The latter found that [32P]phosphorylcholine and -ethanolamine administered by subarachnoid injection, as such or as their cytidine diphosphate esters, were incorporated into their corresponding phospholipids. However, the rate of hydrolysis of the injected material was such that, after 20 min, very little of the ester remained in the brain. KANFER and GAL (1966) injected tritiated erythroand threo-sphingosine intracerebrally and showed that they were incorporated into the sphingomyelin of the 9-day-old rat. In a recent paper ABDEL-LATE and ABOOD (1966) showed that, when serine labelled with 14C in different parts of the molecule was injected, only the DL-[~-'~C] compound was incorporated almost exclusively into phosphatidylserine. The fact that serine enters into many metabolic pathways does not make it a very suitable precursor for studies of this type, and it is not clear from this paper whether any of the label was incorporated into glycerol. In the present paper, experiments on the fate of intracerebrally injected ethanolamine are described. As far as we are aware such experiments have not been carried out previously. Preliminary reports have been given ( SPANNER, 1965, 1966). Materials. [1,2-14C]Ethanolamine hydrochloride was obtained from Calbiochem Ltd., 94 York Street, London W.l. and [2-14C]ethanolamine hydrochloride from the Radiochemical Centre, Amersham, Bucks, England. Pho~phoryl[2-~~C]ethanolamine, was prepared as described for the SaP-labelled compounds (ANSELL and CHOJNACKI, 1966). CDP-[I ,2-14C]ethanolamine was prepared enzymically by the method of CHOJNACKI and METCALFE (1966). The purity of the radioactive chemicals was checked by paper chromatography just before...

[Me-(14)C]Choline was injected intracerebrally into the adult rat, and its uptake into the lipids and their water-soluble precursors in brain was studied. The radioactivity could be detected only in the choline-containing lipids and was confined to the base choline. The results indicated that initial phosphorylation of the free choline followed by the formation of CDP-choline and the subsequent transfer of the phosphorylcholine to a diglyceride is one of the principal routes by which choline lipids in brain are formed. Further evidence for this was obtained in experiments in which either phosphoryl[Me-(14)C]choline or [(32)P]orthophosphate was injected and the radioactivity in the choline-containing water-soluble and lipidbound components studied.

No abstract

Both choline kinase and ethanolamine kinase are present in the cytosol of nerve endings prepared from rat brain are the products of their action, phosphocholine (84 nmol/g fresh wt. of brain) and phosphoethanolamine (190 nmol/g fresh wt. of brain). In contrast with the enzymes from the cytosol of whole brain, both are as equally active at pH 7.5 as 9.0. Determination of kinase activity in membrane-containing tissue samples at pH9 gives low values because of the activity of alkaline phosphatase. Choline kinase, but not ethanolamine kinase, requires Mg2+ in excess of that required for the formation of the MgATP complex and is inhibited by an excess of free ATP. The Km for choline is 2.6mM and for ethanolamine is 2.2mM. The differing requirements for ATP and Mg2+ and the inhibition of choline kinase, but not ethanolamine kinase, by hemicholinium-3 suggest either the presence of two separate enzymes or two different active sites on the same enzyme.