AMP-deaminase from goldfish white muscle: regulatory properties and redistribution under exposure to high environmental oxygen level.

AMP-deaminase was partially purified from white skeletal muscle of goldfish, Carassius auratus. The enzyme was highly stable, showing virtually no change in activity at 1 month following the purification process when stored in 1 M KCl at 2-4 degrees C. The specific activity of the purified enzyme was 130-150 U/mg protein, with a pH optimum of about pH 6.5. AMP-aminohydrolase (AMPD) showed non-Michaelis-Menten kinetics, with a S(0.5) (half saturation by the substrate) for AMP of 0.73 +/- 0.03 mM, a Hill coefficient of 2.01 +/- 0.26, and a V(max) (maximum velocity) of 176 +/- 46 U/mg protein. Both sodium and potassium ions activated goldfish AMPD at low concentrations, with maximal activation at about 80 mM of each chloride salt, whereas higher concentrations became inhibitory. Magnesium and calcium ions also inhibited goldfish muscle AMPD, as did phosphate and fluoride; at a concentration of 8 mM, each anion reduced activity by about 66%. ADP and ATP were strong activators and both demonstrated concentration-dependent activation, with maximal effects at 0.5-1.5 mM. Fish exposure to a high concentration of oxygen (18-20 mg/l against 5-6 mg/l in the control) and recovery to the initial level induced a redistribution of AMPD between free and bound forms in goldfish white muscle and brain in a tissue-dependent manner. A spatial-temporal redistribution may be among the mechanisms regulating enzyme operation in vivo. Possible regulatory mechanisms of AMP-deaminase function in fish muscle are discussed.