Phosphoenolpyruvate carboxykinase (GTP) (EC 18.104.22.168) from rat liver cytosol is activated by micromolar concentrations of Mn2+ under conditions where GTP is present as the MgGTP complex and free Mg2+ is present in excess. The purified, homogeneous enzyme rapidly loses the ability to be activated by Mn2+ upon storage, incubation with oxidized glutathione, or incubation with Mn2+. These changes are prevented by reducing agents. Under certain conditions, phosphoenolpyruvate carboxykinase (Mr = 72,000) co-purifies with a protein of Mr = 29,000. This complex co-elutes on gel permeation chromatography but can be separated by chromatography on GTP-agarose in the presence of Mn2+. The Mr = 29,000 protein stabilizes the activity of the enzyme and protects against the changes which lead to the loss of the Mn2+ activation. These results suggest that the Mn2+ activation of P-enolpyruvate carboxykinase is dependent on the degree of oxidation of cysteine sulfhydryls. The role of the Mr = 29,000 protein in in vitro experiments is to stabilize the enzyme oxidation state which permits activation by Mn2+.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - Nov 10 1981|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology