Abstract
1. 1. AMP-deaminase (EC 3.5.4.6. AMP-aminohydrolase) isolated from beef heart was found to show sigmoid-shaped kinetics at a high (100mM) and low (10mM) potassium ions concentration. Addition of ATP or ADP to the incubation medium changed the kinetics of the reaction to hyperbolic. 2. 2. In the presence of high potassium ions concentration ATP and ADP caused a significant increase of the enzyme-substrate affinity. The calculated values of maximum velocity of the reaction were the same both in the presence and in the absence of activating nucleotides. 3. 3. When 10 mM potassium was present in the incubation mixture, the activating effect of ATP and ADP was more complexed. Both these nucleotides increased not only the enzyme-substrate affinity. but also the maximum velocity and thus catalytic efficiency of the enzyme in these conditions. 4. 4. ATP was shown to be a much more efficient activator of the enzyme than ADP both at low and high potassium concentrations. 5. 5. It is concluded that at a high potassium ions concentration AMP-deaminase from beef heart is regulated by ATP and ADP in the way corresponding to the “ K m -type” of enzyme, whereas a mixed “ K m V-type” of the regulation is observed at low potassium ions concentration.
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