Identification of two cytosolic diacylglycerol kinase isoforms in rat brain, and in NIH-3T3 and ras-transformed fibroblasts

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Abstract
Two major species of diacylglycerol kinase (type I and type II) were separated from brain cytosol and from NIH-3T3 or ras-transformed 3T3 cells by heparin-agarose chromatography. Multiple species of diacylglycerol kinase were also detected by non-denaturing isoelectric focusing. The two peaks of activity were of similar size, both co-eluted at approximately 95 kDa from a Superose f.p.l.c. column. Type II enzyme (pI 8.0) was more active when substrate was presented in a deoxycholate/phosphatidylserine undefined environment, as opposed to an octyl glucoside/phosphatidylserine micellar environment. Type II activity was also enhanced by the presence of phosphatidylcholine as cofactor. Type I enzyme (pI 4.0) was more active in the presence of either phosphatidylserine or phosphatidylinositol. Type I and II enzymes had different ATP affinities. Both enzymes showed a preference for diacylglycerol substrates with saturated acyl chains of 10-12 carbon atoms. The cytosolic enzyme activity was able to bind to diacylglycerol-enriched membranes in NIH-3T3 fibroblasts, and this translocation was unaffected in ras-transformed 3T3 cells. These results demonstrate the presence of multiple diacylglycerol kinases in brain cytosol and NIH-3T3 and ras-transformed 3T3 cells. The enzymes differ in cofactor, ATP and substrate requirements. These results can explain some of the contradictions between previous studies of cytosolic diacylglycerol kinase activity, and suggest the presence of a family of such kinases that are differentially regulated by phospholipid cofactors.