AMP deaminase binding in rat skeletal muscle after high-intensity running.
Skeletal muscle deaminates a substantial fraction of its adenylate pool to inosine 5'-monophosphate (IMP) when the rate of energy expenditure exceeds supply. How AMP deaminase is activated in vivo is unclear because the substrate affinity is quite low (Michaelis constant approximately 1-2 mM) relative to estimated concentrations of free AMP in skeletal muscle (0.2-1 microM). AMP deaminase:myosin binding causes a large increase in substrate affinity; whether this binding occurs during physiological exercise is uncertain. Exhaustive high-speed (60 m/min) treadmill exercise in rats results in an extensive depletion of adenine nucleotide and a stoichiometric accumulation of IMP (1.5-2 mumol/g) in the superficial vastus lateralis muscles (predominantly fast-twitch white). We measured AMP deaminase:myosin binding after intense exercise and found the bound fraction of AMP deaminase to be increased from 9 +/- 1% at rest to 48 +/- 4% at approximately 45 s after exercise. The extent of binding lessened during recovery from exercise, falling to 32 +/- 4% after approximately 75 s and 21 +/- 2% after approximately 105 s. This postexercise dissociation of AMP deaminase from myosin appeared to be a first-order process (approximately 50 s half time). Treadmill running that leads to deamination also results in AMP deaminase:myosin binding. Binding should activate AMP deaminase and thus favor IMP formation at low physiological concentrations of AMP.
Rundell
K W
KW
Department of Physiology, State University of New York, Health Science Center, Syracuse 13210.
Tullson
P C
PC
Terjung
R L
RL
D000659:AMP Deaminase / Q000378:metabolism*; D000818:Animals; D007291:Inosine Monophosphate / Q000378:metabolism; D008297:Male; D009132:Muscles / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism; D005082:Physical Exertion / Q000502:physiology*; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D012420:Running
D007291:Inosine Monophosphate; D000659:AMP Deaminase; D009218:Myosins