Glutathione‐protein mixed disulfide decreases the affinity of rat liver fatty acid‐binding protein for unsaturated fatty acid

Abstract

0.16 .+-. 0.062% of the fatty acid-binding protein purified from 50 mM N-ethylmaleimide-treated rat liver (L-FABP) was determined as a form S-thiolated by glutathione (L-FABP-SSG). L-FABP-SSG, which was prepared in vitro through thiol-disulfide exchange reaction, showed more acidic pI (.apprxeq. 5.0) than the pI (.apprxeq. 7.0) of reduced L-FABP. S-thiolation of L-FABP by glutathione decreased the affinity of the protein for unsaturated fatty acids without changing the equimolar maximum binding. The changes in Kd were from 0.63 .+-. 0.054 .mu.M to 1.03 .+-. 0.14 .mu.M for oleic acid, from 0.63 .+-. 0.028 .mu.M to 0.97 .+-. 0.12 .mu.M for linoleic acid and from 0.85 .+-. 0.050 .mu.M to 1.45 .+-. 0.024 .mu.M for arachidonic acid. This modification did not alter the affinity nor the maximum binding for saturated fatty acids, which were determined to be Kd of .apprxeq. 1.0 .mu.M for palmitic acid and .apprxeq. 0.9 .mu.M for stearic acids, and equimolar maximum binding for both fatty acids. The binding affinity of L-FABP for unsaturated fatty acid may be regulated by redox state of the liver.