When a 100000 ×g supernatant from bovine heart was incubated with [1-14C]oleic acid and subjected to isoelectric focusing, two fatty acid binding proteins (FABPs) with isoelectric points at 4.9 and 5.1 were detected.



The proteins were purified on a large scale first by heat and acid precipitation of a postmitochondrial supernatant, as well as fractionation with ammonium sulfate, then by alternate application of ion-exchange and gel chromatography. The procedure afforded around 60 mg pure proteins from 1.5 kg fresh heart muscle.



Relative molecular masses of 15 300 ± 1600 for both proteins were derived from sodium dodecyl sulfate/polyacrylamide gel electrophoresis, gel chromatography, sedimentation velocity as well as from amino acid analysis. Up to 50% of the proteins' secondary structures consisted of β-sheet. N-termini of the peptide chains were blocked; the amino acid compositions of the two proteins were similar, but differed considerably from those of the two FABPs isolated from bovine liver [Haunerland et al. (1984) Hoppe Seyler's Z. Physiol. Chem. 365, 365–376]. Whereas hepatic FABPs changed their pI upon binding fatty acids, cardiac FABPs did not. Cardiac FABPs were immunologically identical, but did not cross-react with hepatic proteins.



A reversible, concentration-dependent self-association reported for FABP from pig heart [Fournier et al. (1983) Biochemistry 22, 1863–1872] was not observed for FABP from bovine heart. Changes of concentration did not alter secondary structure, intrinsic fluorescence or the sedimentation coefficient of the protein.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1985.tb09229.x

Bovine fatty acid binding proteins

Regulation intracellular cholesterol transport is not well understood. Part of the difficulty is that not only is the intracellular distribution of cholesterol not uniform, but even within membranes cholesterol has an asymmetric transbilayer and lateral distribution. Although both vesicular and protein mediated pathways for cholesterol movement are recognized, the role of intracellular cholesterol binding proteins in cytosolic cholesterol trafficking remains largely unresolved. Recent work from this and other laboratories demonstrates that these cholesterol binding proteins are involved in cholesterol uptake and intracellular trafficking. Immunocytochemical evidence supports the presence of significant amounts of proteins such as the sterol carrier protein-2 outside of peroxisomes.

Intracellular Sterol Binding Proteins: Cholesterol Transport and Membrane Domains

Purification of Sterol Carrier Protein (SCP) from rat liver is described. Lipid binding studies indicated that the purified SCP is a fatty acid binding protein. However, no cholesterol binding by SCP was observed. Antibodies were produced in both mice and rabbits to PAG-incorporated SCP and to native SCP and the specificity and sensitivity of two of the antisera was determined to be adequate for development of an ELISA for SCP. Further treatment of the selected antisera is discussed with a view to development of a sandwich ELISA for SCP.

Studies on sterol carrier protein

The endogenous lipid pattern of a fatty acid binding protein (FABP; synonym: "Z"-protein) in the cytosolic fraction of rat liver involves besides "free" fatty acids also phospholipids and mono-, di- and triacylglycerols. The relation between "free" fatty acids and the sum of all other lipids is nearly 1. In consequence of this result a correction of the idea is necessary that the FABP specifically binds only fatty acids. With immunological techniques it has been shown that the FABP has no organ-specificity and no immunological relation to the lipoproteins of the serum. A high content of fat in the diet (25% fat) compared with a low fat content of the diet (1% fat) led to an increase of the concentration of FABP in the cytosols of different rat organs (liver, intestinal mucosa, fat tissue and heart). Therefore a physiological function in the intracellular translocation of the fatty acids in different rat organs was inferred.

Risse S

Papers

[Endogenous lipid pattern, organ distribution and effect of diet on a fatty acid binding protein fraction of rat liver cytosol].