Interactions of oleic acid with liver fatty acid binding protein: a carbon-13 NMR study.
13C NMR spectroscopy was used to probe the structural interactions between carboxyl-13C-enriched oleic acid (18:1) and rat liver fatty acid binding protein (FABP) and the partitioning of 18:1 between FABP and unilamellar phosphatidylcholine (PC) vesicles. Spectra of systems containing 2-8 mol of 18:1/mol of FABP (but no PC) exhibited one carboxyl resonance (182.2 ppm) corresponding to FABP-bound 18:1. At pH values less than 8.0, an additional carboxyl resonance, corresponding to unbound 18:1 in a lamellar phase, was observed. Both resonances exhibited ionization shifts with estimated apparent pKa values of less than 5 (bound 18:1) and greater than 7 (unbound 18:1). The intensity of the resonance corresponding to FABP-bound 18:1 increased with increasing 18:1/FABP mole ratio and at 8/1 mole ratio indicated that at least 2 and 6 mol of 18:1/mol of FABP were FABP-bound at pH 7.4 and 8.6, respectively. NMR spectra of systems containing equal concentrations (w/v) of FABP and PC and from 1 to 4 mol of total fatty acid (FA)/mol of FABP exhibited two 18:1 carboxyl resonances (182.2 and 178.5 ppm, pH 7.4). The downfield resonance corresponded to FABP-bound 18:1 and the upfield resonance to PC vesicle bound 18:1. At 1/1 mole ratio (FA/FABP), the intensities of both resonances were approximately equal, but at 4/1 mole ratio the resonance for PC vesicle bound 18:1 was 3-fold more intense than that for FABP-bound 18:1. The following conclusions are reached: (i) The carboxyl groups of 18:1 bound to liver FABP experience only one type of binding environment (the aqueous milieu adjacent to the protein surface).(ABSTRACT TRUNCATED AT 250 WORDS)
Cistola
D P
DP
Housman Medical Research Center, Department of Biochemistry, Boston University School of Medicine, Massachusetts 02118.
Walsh
M T
MT
Corey
R P
RP
Hamilton
J A
JA
Brecher
P
P
D000818:Animals; D002247:Carbon Isotopes; D002352:Carrier Proteins / Q000378:metabolism*; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D019301:Oleic Acid; D009829:Oleic Acids / Q000378:metabolism*; D051381:Rats
D002247:Carbon Isotopes; D002352:Carrier Proteins; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D009829:Oleic Acids; D019301:Oleic Acid