The influence of phosphate, fluoride and potassium ions on the activity of amp-deaminase from human skeletal muscle

1. 1. Kinetic properties of the inhibitory effect of inorganic phosphate and fluoride and of the activatory effect of potassium ion on human skeletal muscle AMP-deaminase (E.C. 3.5.4.6) have been investigated 2. 2. It has been shown that phosphate is a competitive inhibitor ( K 1 , ≈0.8 × 10 −3 M) and fluoride a noncompetitive inhibitor ( K 1 ≈3.2 × 10 −3 M) of human muscle AMP-deaminase. 3. 3. The changes of potassium ion concentration between 20 and 200 mM did not influence the Michaelis constant which was about 0.9 x 10 −3 M at 30°C. Also the change of substrate concentration in the range 40–300 μM did not influence the activation constant for potassium ( K a ≈0.4 × 10 −1 M). 4. 4. Higher concentraion of potassium (200mM) was found to diminish the “temperature sensitivity” of the enzyme activity. 5. 5. The energy of activation (E) in the presence of 150 mM KC1 calculated from Arrhenius plot was about 4600 cal/mole of substrate. The heat of the enzyme-substrate complex formation obtained from the plot of log K m vs T −1 was shown to have positive value (+2200 cal/mole) at the temperatures lower than 23°C and negative value (—4100 cal/mole) at the temperatures higher than 23°C.