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.
Department of Physiology, State University of New York, Health Science Center, Syracuse 13210.
K W
KW
Rundell
P C
PC
Tullson
R L
RL
Terjung
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