FATTY-ACID-BINDING PROTEIN - STIMULATION OF MICROSOMAL PHOSPHATIDIC-ACID FORMATION

The effect of fatty acid binding proteins (FABPs) on two key steps of microsomal phosphatidic acid formation was examined, Rat liver microso mes were purified by size-exclusion chromatography to remove endogenou s cytosolic fatty acid and fatty acyl-CoA binding proteins while recom binant FABPs were used to avoid cross-contamination with such proteins from native tissue. Neither rat liver (L-FABP) nor rat intestinal fat ty acid binding protein (I-FABP) stimulated liver microsomal fatty acy l-CoA synthase. In contrast, L-FABP and I-FABP enhanced microsomal con version of [C-14]oleoyl-CoA and glycerol 3-phosphate to [C-14]phosphat idic acid by 18- and 7-fold, respectively. The mechanism for this stim ulation, especially by I-FABP, is not known. However, several observat ions presented here suggest that, like L-FABP, I-FABP may interact wit h fatty acyl-CoA and thereby stimulate enzyme activity. First, I-FABP decreased microsomal membrane-bound oleoyl-CoA. Second, oleoyl-CoA dis placed I-FABP bound fluorescent fatty acid, cis-parinaric acid, with K -i of 5.3 mu M and 1.1 sites. Third, oleoyl-CoA decreased I-FABP trypt ophan fluorescence with a K-d of 4.2 mu M. Fourth, oleoyl-CoA red shif ted emission spectra of acrylodated I-FABP, a sensitive marker of I-FA BP interactions with ligands. In summary, the results demonstrate for the first time that both L-FABP and I-FABP stimulate liver microsomal phosphatidic acid formation by enhancing synthesis of phosphatidate fr om fatty acyl-CoA and glycerol 3-phosphate. (C) 1997 Academic Press.