Synthesis and turnover of brain phosphoglycerides- results, methods of calculation and interpretation.

The important problem of membrane assembly and disassembly can be studied by measurements of rates of tunrover of labeled components. After intracerebral injections of ethanolamine and glycerol into mice, we have found rapid and slow turnover pools of 1,2-diacyl-sn-glycero-3-phosphorylethanolamine (diacyl-GPE) and 1,2-diacyl-sn-glycero-3-phosphorylcholine (diacyl-GPC). We have described the methods for calculation of half-lives for two or more pools and for the calculation of the relative size of the pools. For mice injected between 5 and 8 weeks of age, the rapid turnover pools have a half-life of 1.5 and 1.8 days for diacyl-GPC and diacyl-Ge respectively. Corresponding half-lives for the slow turnover pools are 20 and 27 days. The slow turnover pools include 74% of the diacyl-GPC and 86% of the diacyl-Ge. These turnover rates are in agreement with the flux of fatty acids through the diacylglycerol pools. We have proposed that the rapid turnover pool may be the phosphoglycerides that are exchangable with cytosol carrier proteins and that the slow turnover may represent the catabolism of membrane segments including the intrinsic proteins.