Importance of proline and other amino acids during honeybee flight
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The levels of proline and other amino acids in the haemolymph and other body parts of honeybee foragers were investigated by HPLC analysis. The concentrations of proline in the blood of glucose-fed or -injected bees finishing their exhaustive tethered flights on a roundabout were significantly reduced compared to bees that were fed and rested for one hour. This indicates some utilization of proline during flight metabolism. The levels of essential amino acids and of the sum of all amino acids except proline remained roughly constant, indicating that the decrease of proline did not result from a changed haemolymph volume. 14C-labelled proline was injected into bees either shortly before starting their flight or before a resting period of equal duration in an incubator at the same temperature. Bees that rested had incorporated more proline into thorax body protein, and less of the labelled substance was unrecovered ("missing") and considered to be respired or less probably defecated. If the entire amount of missing 14C-proline is regarded as exhaled, the oxidative breakdown of proline reached higher levels after flight than in rested bees. This is another hint that proline is utilized during flight. Usually the exhaled amount did not exceed 10 μg proline in half an hour of flight. Although our data indicate involvement of proline in flight metabolism, the amount metabolized is low compared to the utilization of carbohydrates.
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