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First published online January 27, 2004
Journal of Experimental Biology 207, 749-754 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00825
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`Futile cycle' enzymes in the flight muscles of North American bumblebees

James F. Staples*, Erin L. Koen{dagger} and Terence M. Laverty

Department of Biology, University of Western Ontario, London, Ontario, Canada, N6A 5B7

* Author for correspondence (e-mail: jfstaple{at}uwo.ca)

Accepted 8 December 2003

In the flight muscles of European bumblebees, high activities of fructose-1,6-bisphosphatase (FbPase) relative to phosphofructokinase (PFK) have suggested a thermogenic `futile cycle' important for regional endothermy. We find generally low activities of FbPase (0.7-19.7 units g-1 thorax) in North American Bombus species, with the exception of Bombus rufocinctus, where activity (43.1 units g-1 thorax) is comparable with that of European congeners. These data, taken with estimates of maximal rates of heat production by cycling, do not support a significant thermogenic role for the PFK/FbPase cycle. In agreement with earlier studies, both PFK and FbPase activities were found to scale allometrically with body size (allometric exponents -0.18 and -1.33, respectively). The cycle may serve to supplement thermogenesis or amplify glycolytic flux in rest-to-flight transitions, especially in smaller bees.

Key words: thermogenesis, flight muscle, fructose-1,6-bisphosphatase, phosphofructokinase, futile cycle, enzyme, bumblebee, Bombus


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© The Company of Biologists Ltd 2004