AMP DEAMINASE BINDING IN RAT SKELETAL-MUSCLE AFTER HIGH-INTENSITY RUNNING

Skeletal muscle deaminates a substantial fraction of its adenylate poo l to inosine 5'-monophosphate (IMP) when the rate of energy expenditur e exceeds supply. How AMP deaminase is activated in vivo is unclear be cause the substrate affinity is quite low (Michaelis constant approxim ately 1-2 mM) relative to estimated concentrations of free AMP in skel etal muscle (0.2-1 muM). AMP deaminase:myosin binding causes a large i ncrease in substrate affinity; whether this binding occurs during phys iological exercise is uncertain. Exhaustive high-speed (60 m/min) trea dmill exercise in rats results in an extensive depletion of adenine nu cleotide and a stoichiometric accumulation of IMP (1.5-2 mumol/g) in t he superficial vastus lateralis muscles (predominantly fast-twitch whi te). 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 e xtent 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 appear ed to be a first-order process (approximately 50 s half time). Treadmi ll running that leads to deamination also results in AMP deaminase:myo sin binding. Binding should activate AMP deaminase and thus favor IMP formation at low physiological concentrations of AMP.