Molecular species of fatty acid binding protein and their function in lipid metabolism

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1. Molecular species of FABP and their tissue distribution:FABPs purified from rat brain and heart cytosol are immunologically unrelated to L-FABP and no L-FABP is present in either rat brain or heart cytosol. Thus, the ex= pression of FABP molecular species seems to be tissue specific. immunohistochemical studies revealed that the distribution pattern of the positive hepatocytes was uniform throughout the acini in fetuses but periportal in abults. In the rat intestine, the expression of L-FABP was changed in the course of ipithelial cell differentiation.2. Properties of charge isoforms and the function of FABPs:The origin of charge isoforms of L-FABP was partly explained by the covalent modi= fication of cysteine at 69 and by the molecular species of bound fatty acid.There are no difference in oleic acid binding to L-FABP and H-FABP. Binding of oleoyl DoA to H-FABP was nonsaturable process, possibly explained by nonspecific association of oleoyl CoA aggregates with H-FABP. On the other hand, there was specific and saturable binding of oleoyl CoA to L-FABP involving a single binding site per mole.Acly CoA synthetase activity of cell particulates was increased by the addition of L-FABP but not H-FABP, when fatty acid was added as the mixed phosphatidylcholine lipo= somes. The preference of H-FABP to heart cell particulates and L-FABP to liver cell particulates was demonstrated when acyl CoA synthetase activity was assayed using fatty acid-FABP complex as substrate.3. Cell response:DG-kinase which is involved in cell response of arachidonate release was purified from pig brain cytosol. Immunological studies show that DG-kinase is present in the cytosol as well as microsomal and synaptosomal membranes of the brain. Immunostaining of-brain tissues demonstrated that neurons were positively stained whereas glial cells were not stained. Although the extent of enzyme phosphorylation was limited, the results show that DG-kinase can be a phosphoprotein.