Locust flight metabolism studied in vivo by 31P NMR spectroscopy

Flight metabolism of locusts has been extensively studied, but biochemical and physiological methods have led to conflicting results. For this reason the non-invasive and non-destructive method of ³¹P NMR spectroscopy was used to study migratory locusts, Locusta migratoria, at rest and during flight.

1.	In the flight muscle of resting locusts the ratio of phosphoarginine to ATP was the same whether determined by NMR (1.76) or biochemically, but the NMR-visible content of inorganic phosphate (Pi) was only 40% of ATP, i.e., much lower than total Pi as determined biochemically. This suggests that most of the Pi in flight muscle is not free, and hence not available as substrate or effector for cytosolic enzymes. Similarly, the free content of ADP and AMP in resting muscle was calculated to be much lower than the total content.
2.	Flight brought about a marked increase in Pi and a decrease in phosphoarginine in flight muscle although there was no change in intracellular pH.
3.	At the initiation of flight a new steady state of ATP, Pi, and phosphoarginine was rapidly established and minimal changes occurred after the first 2 s of flight.
4.	From the free contents of ATP and phosphoarginine in working flight muscle the flight-induced fractional increases in free ADP and free AMP were calculated to be 5.0-fold and 27.4-fold, respectively. As Pi, ADP, and AMP are substrates and potent effectors of enzymes, the flight-induced increase in their contents is likely to have marked effects on metabolic flux in working muscle.
5.	After short-term flight as well as prolonged flight, phosphoarginine, ATP, and Pi returned rapidly to their preflight levels, indicating that metabolic recovery from flight is rapid.
6.	The locust appears to be an appropriate model for the study of metabolic regulation in aerobic muscle during exercise.

Dedicated to Professor Dr. Ernst Zebe (University of Münster) on occasion of his 65^th birthday.