'Futile cycle' enzymes in the flight muscles of North American bumblebees.
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.
Staples
James F
JF
Department of Biology, University of Western Ontario, London, Ontario, Canada, N6A 5B7. jfstaple@uwo.ca
Koen
Erin L
EL
Laverty
Terence M
TM
D000818:Animals; D001516:Bees / Q000201:enzymology* / Q000502:physiology; D001824:Body Constitution; D005426:Flight, Animal; D006597:Fructose-Bisphosphatase / Q000378:metabolism / Q000502:physiology*; D018482:Muscle, Skeletal / Q000201:enzymology*; D009656:North America; D025221:Phosphofructokinases / Q000378:metabolism; D015219:Substrate Cycling / Q000502:physiology; D022722:Thermogenesis / Q000502:physiology
D025221:Phosphofructokinases; D006597:Fructose-Bisphosphatase