title: Substrate-dependent dissociation of malate thiokinase.
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.
mesh_terms: D000105:Acetyl Coenzyme A; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D003065:Coenzyme A; D003066:Coenzyme A Ligases / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008293:Malates; D008970:Molecular Weight; D010766:Phosphorylation; D011549:Pseudomonas / Q000201:enzymology
chemical_list: D046911:Macromolecular Substances; D008293:Malates; D000244:Adenosine Diphosphate; D000105:Acetyl Coenzyme A; D000255:Adenosine Triphosphate; D003066:Coenzyme A Ligases; C021537:malate - CoA ligase; D003065:Coenzyme A