Abstract
Malate thiokinase has been purified to apparent homogeneity by employing conventional purification techniques along with affinity chromatography. The enzyme is composed of two nonidentical subunits (alpha subunit Mr=34,000, beta subunit Mr=42,500) to yield an alpha 4 beta 4 structure for the native enzyme. Phosphorylation of the enzyme by ATP occurs exclusively on the alpha subunit. The phosphorylated enzyme is acid labile and base stable consistent with phosphorylation of a histidine residue. Dephosphorylation of the enzyme is promoted by ADP, succinate, malate, and coenzyme A plus inorganic phosphate. Phosphorylation of the enzyme leads to a reversible change in the sedimentation properties of the enzyme; the native enzyme exhibits an S20,w of approximately 10, whereas the phosphoenzyme exhibits an S20,w of approximately 7. Formation of the 7 S form of the enzyme is also observed when coenzyme A and succinyl-CoA interact with the enzyme. The ratio of alpha to beta subunits in both the 10 S and 7 S forms of the enzyme is approximately 1.0, suggesting that the 7 S form of the enzyme has an alpha 2 beta 2 structure.
Original language | English |
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Pages (from-to) | 2434-2438 |
Number of pages | 5 |
Journal | Journal of Biological Chemistry |
Volume | 254 |
Issue number | 7 |
State | Published - Apr 10 1979 |
ASJC Scopus subject areas
- Biochemistry
- Molecular Biology
- Cell Biology