PURIFICATION AND CHARACTERIZATION OF FATTY-ACID-BINDING PROTEINS FROMBROWN ADIPOSE-TISSUE OF THE RAT

Fatty acid-binding proteins (FABPs) have been identified and purified from interscapular brown adipose tissue of the rat. The proteins were characterized and their properties compared with the FABP present in w hite adipose tissue. FABP was purified to electrophoretic homogeneity from brown adipose tissue by a procedure involving precipitation with 70% ammonium sulphate, followed sequentially by ion-exchange chromatog raphy and gel filtration chromatography. The purified fraction migrate d as a single band on SDS-PAGE with an apparent molecular mass of 1420 0. Scatchard analysis of [C-14]oleate-binding to purified FABP gave a Kd value of approx. 0.80 +/- 0.02 muM and a maximal binding of 0.65 +/ - 0.03 mol per mol of protein; these values were similar to that found with the FABP purified from white fat. The FABP concentration in brow n adipose tissue was almost twice that of FABP in white adipose tissue . Fatty acid analysis of FABP from brown adipose tissue revealed that the intrinisic arachidonic acid content was proportionately higher tha n that present in FABP of white adipose tissue. Isoelectric focusing o f delipidated FABP indicated that it existed with two charge isoforms (pl 6.85 and 7.35). The purified FABP additionally emerged in two peak s (FABP-I and FABP-II) from a reverse phase HPLC column. Amino acid an alysis showed that Gly, Thr, and Ser residues in FABP-I were almost tw ice as high as in FABP-II. The N-terminals of both FABP-I and -II were not blocked. These components have been partially sequenced and showe d a sequence homology only between 25-31 residues from the N-terminal. Further studies are required to elucidate the precise function of the two different isoforms of FABP in brown adipose tissue.