The Activation of Muscle Hexokinase by Divalent Metal Ions.

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Abstract
Muscle hexokinase which is rapidly inactivated in solution, can to some extent by stabilized by EDTA and pyrophosphate. A procedure involving fractionation with ethanol is described for the partly purification of muscle hexokinase. The activation of the enzyme by different divalent metal ions has been investigated. The highest maximal activity was obtained by Mg and at a molar ratio of Mg2+/ATP = 1. Sodium pyrophosphate inhibits hexokinase apparently by the formation of a Mg-pyrophosphate complex, which excludes Mg2+ from the activated enzyme substrate complex. In addition, an inhibition of hexokinase by a 11 magnesium pyrophosphate complex has been shown. The kinetics of this inhibition is in accordance with a competitive type with respect to the Mg [long dash] ATP complex. This gives support for the assumption that the Mg [long dash] ATP complex is the actual substrate for muscle hexokinase. At increased concentrations of ATP-4 and Mg2+ the enzyme activity is inhibited. Muscle hexokinase is in addition activated by Ca2+, Co2+, Mn2+, and to a small extent by Zn2+. In comparison with the Mg2+ effect the activation by these metal ions is characterized as follows. Maximal enzyme activity is less. Activa-tion does occur at low concentration of these metals and at a molar ratio Me2+/ATP considerable below 1. Half maximal activity for Co2+ and Mn2+ is observed at a concentration 10 times lower than for Mg2+. At increased concentration of these metal ions, strong inhibition of the enzyme activity is observed.
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