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First published online September 9, 2005
Journal of Experimental Biology 208, 3573-3579 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01775

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Energy metabolism in orchid bee flight muscles: carbohydrate fuels all

Raul K. Suarez¹, Charles-A. Darveau^2,*, Kenneth C. Welch, Jr.¹, Diane M. O'Brien³, David W. Roubik⁴ and Peter W. Hochachka^2,

¹ Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106-9610, USA
² Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
³ Biology and Wildlife Department, University of Alaska, Fairbanks, AK 99775, USA
⁴ Smithsonian Tropical Research Institute, Balboa, Republic of Panama

View larger version (16K): [in a new window]   Fig. 1. Oxygen consumption in vitro by thoracic homogenate from a 1.11 g Eulaema bombiformis. 50 µl samples were injected into 1.60 ml of assay medium. 20 µl of 40 mmol l-1 ADP was injected where indicated. No stimulation of respiration by ADP is observed when substrates provided are 0.03 mmol l-1 palmitoyl L-carnitine + 6 mmol l-1 proline. Injection of ADP results in stimulation of respiration when 6 mmol l-1 pyruvate + 6 mmol l-1 proline are provided as substrates. The slope of the linear part of the trace after ADP injection yields a rate of 144 nanoatoms O min-1. Note the break at the end of the ADP-stimulated (state 3) rate and the beginning of a lower (state 4) rate, as would normally be expected after depletion of ADP. Because our protocol makes use of crude homogenates, the state 4 rate is still high relative to the state 4 rates obtainable with isolated, well-coupled, mitochondria. In addition, such transitions between state 3 and state 4 rates were not always observed. This is to be expected, given the high contaminating ATPase activities found in tissue homogenates. This limitation in our protocol precluded meaningful estimates of respiratory control (state 3/state 4) and ADP/O ratios.

View larger version (21K): [in a new window]   Fig. 2. Proposed pathways for substrate oxidation in bees, showing roles played by fat body, hemolymph, cytoplasmic and mitochondrial reactions. Not all reactions are included and details concerning individual reactions are left out to emphasize the main routes of carbon flow, the glycerol 3-phosphate (G3P) shuttle, and anaplerotic (pyruvate carboxylase and proline oxidation) reactions. Abbreviations are as follows: Pi, inorganic phosphate, G6P, glucose 6-phosphate, F6P, fructose 6-phosphate, FDP, fructose 1,6-diphosphate, DHAP, dihydroxyacetone phosphate, GAP, glyceraldehyde 3-phosphate, pyr, pyruvate, G3P, glycerol 3-phosphate, H, reducing equivalent, OXA, oxaloacetate, CIT, citrate, KG, alpha-ketoglutarate, glut, glutamate, PROL, proline, CYTO, cytoplasmic compartment, MITO, mitochondrial matrix.