The muscle fatty acid binding protein of spadefoot toad (Scaphiopus couchii)

Fatty acid binding protein was purified from skeletal muscle of the spadefo ot toad (Scaphiopus couchii), an estivating species. While estivating, this animal relies on the fatty acid oxidation for energy. Hence we were intere sted in the behaviour of fatty acid binding protein under conditions of ele vated urea (up to 200 mM) and potassium chloride such as exist during estiv ation. Also we examined whether there were interactions between glycolytic intermediates and the binding ability of the protein. The amount of bound f atty acid (a fluorescence assay using cis-parinarate) was not affected (P<0 .05) by glucose, fructose 6-phosphate or phosphoenolpyruvate at physiologic al concentrations. By contrast, glucose 6-phosphate increased the amount of bound cis-parinarate but the apparent dissociation constant was not differ ent from the control. Fructose 1,6-bisphosphate but nor fructose 2,6-phosph ate decreased cis-parinarate binding by 40%, commensurate with doubling the apparent dissociation constant (1.15-2.62 mu M). Urea, guanidinium and tri methylamine N-oxide at 200 mM increased cis-parinarate binding 60% over con trols. Urea (1 M) and KCl (200 mM) did not affect cis-parinarate binding co mpared to controls. The interaction of this fatty acid transporter with fru ctose 1,6-bisphosphate is discussed in terms of reciprocal interaction with phosphofructokinase since fatty acid is also an inhibitor of phosphofructo kinase. (C) 2000 Elsevier Science Inc. All rights reserved.