Mammalian mitochondrial glycerol-3-phosphate acyltransferase.

Glycerol-3-phosphate acyltransferase (GPAT) is the first committed, and presumed to be a rate-limiting, step in glycerophospholipid biosynthesis. There are two isoforms of GPAT, a mitochondrial and a microsomal form. Mitochondrial GPAT has recently been purified and its gene has been cloned and expressed in baculovirus-infected cells. The GPAT activity was reconstituted using the purified enzyme and various phospholipids. Mitochondrial GPAT prefers saturated fatty acyl-CoA as a substrate. This preference may contribute to the observed asymmetric distribution of saturated and unsaturated fatty acids at the sn-1 and sn-2 positions of cellular glycerophospholipids. A region of homology to various acyltransferases that may be important for catalysis or fatty acyl-CoA binding is present in mitochondrial GPAT. Mitochondrial GPAT is upregulated at the transcriptional level by refeeding a high carbohydrate, fat-free diet to previously fasted mice and by insulin administration to diabetic animals, whereas microsomal GPAT activity is largely unaffected by these treatments.