Purification and characterization of fatty acid-binding protein from aerobic muscle of the Antarctic icefish Chaenocephalus aceratus.

Intracellular fatty acid-binding protein is purified and characterized from aerobic skeletal muscle of the Antarctic icefish Chaenocephalus aceratus. Molecular mass of C. aceratus FABP (CA-FABP) is 14,936 Da as estimated by electrospray mass spectrometry. CA-FABP is expressed at an intracellular concentration of 0.984 +/- 0.115 mg CA-FABP g-1 wet weight aerobic muscle and binds 0.859 +/- 0.013 moles oleic acid per mole of protein at a physiological temperature of 0 degrees C. Dissociation constants (KdS for various fatty acid ligands range from 1.38 to 2.71 microM; KdS are not significantly different among palmitic acid (16:0), palmitoleic acid (16:1), and oleic acid (18:1). Competition assays reveal that CA-FABP does not have preferential affinity for the very-long-chain, polyunsaturated fatty acids that are common in Antarctic fish (e.g., docosahexaenoic acid; 22:6). Partial amino acid sequence from CA-FABP aligns with mammalian heart-type FABPs with as high as 74% identity. These data are strikingly similar to mammalian values, yet they are derived from an organism that is distant from mammals in terms of phylogeny, body temperature, and physiology. This suggests that the FABP family is conserved not only in primary sequence, but also in its physiological properties.