| Autor: |
Chrisman, Ted D., Sobo, Gwenn E., Exton, John H. |
| Zdroj: |
FEBS Letters; January 1984, Vol. 167 Issue: 2 p295-300, 6p |
| Abstrakt: |
Incubation of rat liver phosphorylase kinase in the presence of MgATP results in a time-dependent increase in activity, i.e., activation. Determination of the magnitude of activation depends, in large part, on the relative concentrations of Mg 2+and ATP used in the phosphorylase kinase activity assay, such that as the Mg 2+to ATP ratio increases less activation is detectable. Prior to activation, maximal activity of nonactivated phosphorylase kinase requires a 2–3 fold molar excess of Mg 2+(i.e., free Mg 2+) over ATP. MgATP-dependent activation of the enzyme results in an alteration in the free Mg 2+requirement such that the activity of the activated enzyme is sharply inhibited by the free cation. Inhibition by free Mg 2+of the activated enzyme is rapidly reversed by removal of free Mg 2+but is not affected by addition of Ca 2+. Both nonactivated and activated forms of enzyme appear to be inhibited by free ATP 4–. The results show that the use of high concentrations of free Mg 2+in the phosphorylase kinase activity assay can blunt or completely obscure changes in enzyme activity following activation of the enzyme. |
| Databáze: |
Supplemental Index |
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