MODIFICATION OF THE FATTY-ACID-BINDING PROFILE OF LIVER FATTY-ACID-BINDING PROTEIN (L-FABP)

Low molecular-weight fatty acid binding protein (L-FABP) was purified from rat liver by a combination of gel filtration and affinity chromat ography. The purified protein had a molecular weight of 14,000 Daltons as determined by sodium dodecyl sulfate-polyacrylamide gel electropho resis and fast protein liquid chromatography (FPLC) gel filtration chr omatography. Isoelectric focusing of delipidated preparations gave a m ajor protein band with a pI of 7.5. Delipidated L-FABP was used to det ermine binding constants for individual saturated, monounsaturated, an d polyunsaturated fatty acids. For fatty acids of chain length greater than C14 there was no apparent selectivity based on chain length or d egree of unsaturation. When delipidated L-FABP was incubated with an e quimolar (0.3 mmol/L) mixture of fatty acids; 16:0, 18:1 (n-9), 18.2(n -6), 20:3(n-6), 20:4(n-6), and 22:6(n-3) were bound at equivalent leve ls (0. 18 mol/mol L-FABP). However, stearic acid was bound to a greate r extent (approximately two fold) and 18:3(n-6) and 18:3(n-3) were bou nd to a lesser extent (50%). 12:0, 14:0, and 20:5(n-3) bound poorly to L-FABP. Thus, under these conditions fatty acid binding protein exhib its a selectivity that is not apparent from individual binding constan ts. When rats were maintained on different diets for 6 weeks, the conc entration of L-FABP was reduced only in animals maintained on a fat-fr ee diet. The apparent binding capacity of L-FABP (0.71 mol fatty acid per mol L-FABP) was the same for all diets. However, the endogenous fa tty acid composition of L-FABP was strongly influenced by dietary fatt y acid composition.