Comparative Biochemistry and Physiology Part B 125 (2000) 347 – 357 The muscle fatty acid binding protein of spadefoot toad (Scaphiopus couchii ) J.M. Stewart a, *, J.F. Claude a , J.A. MacDonald b , K.B. Storey b a Biochemistry Program, Department of Biology, Mount Allison Uniersity, Flemington Building, 63B York St., Sackille, NB, Canada E4L 1G7 b Institute of Biochemistry and Department of Biology, Carleton Uniersity, Ottawa, Ont., Canada Received 9 August 1999; received in revised form 30 November 1999; accepted 6 December 1999 Abstract Fatty acid binding protein was purified from skeletal muscle of the spadefoot toad (Scaphiopus couchii ), an estivating species. While estivating, this animal relies on the fatty acid oxidation for energy. Hence we were interested in the behaviour of fatty acid binding protein under conditions of elevated urea (up to 200 mM) and potassium chloride such as exist during estivation. Also we examined whether there were interactions between glycolytic intermediates and the binding ability of the protein. The amount of bound fatty acid (a fluorescence assay using cis -parinarate) was not affected (P 0.05) by glucose, fructose 6-phosphate or phosphoenolpyruvate at physiological concentrations. By contrast, glucose 6-phosphate increased the amount of bound cis -parinarate but the apparent dissociation constant was not different from the control. Fructose 1,6-bisphosphate but not fructose 2,6-phosphate decreased cis -parinarate binding by 40%, commensurate with doubling the apparent dissociation constant (1.15 – 2.62 M). Urea, guanidinium and trimethylamine N-oxide at 200 mM increased cis -parinarate binding 60% over controls. Urea (1 M) and KCl (200 mM) did not affect cis -parinarate binding compared to controls. The interaction of this fatty acid transporter with fructose 1,6-bisphosphate is discussed in terms of reciprocal interaction with phosphofructokinase since fatty acid is also an inhibitor of phosphofructokinase. © 2000 Elsevier Science Inc. All rights reserved. Keywords: Amphibian; Estivation; Glycolytic; Metabolism; Control; Phosphofructokinase; Urea; Hypometabolism; Anuran; Lipid www.elsevier.com/locate/cbpb 1. Introduction Many animals survive harsh conditions im- posed by seasonal changes such as extended limi- tations in food, oxygen or water availability and/or adverse temperatures (cold, heat) by enter- ing a hypometabolic state. The biochemical adap- tations required to enter into and sustain a torpid state are gradually being elucidated. For example, mammalian hibernation is accompanied by the establishment of a new homeostasis at tempera- tures that can be 30°C or more below usual body temperature (Wang, 1988; Storey and Storey, 1990). During hibernation, metabolic energy re- quirements, although reduced about 80%, are met primarily by oxidation of fatty acids (FAs) drawn from lipid stores (Frank and Storey, 1995). The challenge of elevated temperatures and decreased water supply, as is found in desert environments, is met by the ability of some lower vertebrates to enter estivation, another variant of the hy- pometabolic state. * Corresponding author. Tel.: +1-506-3642364; fax: +1- 506-3642505. E-mail address: jstewart@mta.ca (J.M. Stewart) 0305-0491/00/$ - see front matter © 2000 Elsevier Science Inc. All rights reserved. PII:S0305-0491(99)00188-1