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When a 100000 x g supernatant from bovine heart was incubated with [l-i4C]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. 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 P-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 A reversible, concentration-dependent self-association reported for FABP from pig heart [Fournier et al. (1983) Biochemistry 22, 1863-18721 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.

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