Pyruvate phosphate dikinase, mechanism

Three enzymes of the C4 pathway are regulated by light, becoming more active in daylight. Malate dehydrogenase is activated by the thioredoxin-dependent reduction mechanism shown in Figure 20-19 PEP carboxylase is activated by phosphorylation of a Ser residue and pyruvate phosphate dikinase is activated by dephosphorylation. In the latter two cases, the details of how light effects phosphorylation or dephosphorylation are not known. 

The problem of focusing phosphorylation free energy is elegantly solved in the mechanisms of action of phosphoenolpyruvate synthetase and pyruvate phosphate dikinase. Phosphohistidyl residues are generated at the active sites of these enzymes by pyrophosphorylation of active site histidines, followed by hydrolysis... 

Hatch,M.D., Osmond,C.B. Compartmentation and transport in C4 photosynthesis. In Transport in plants III. Enzyclopedia of plant physiology. New series, Vol. 3. Stocking, C.R., Heber,U. (eds.), pp. 144-184. Berlin, Heidelberg, New York Springer 1976 Hatch, M.D., Slack, C.R. Studies on the mechanism of activation and inactivation of pyruvate, phosphate dikinase. A possible regulatory role for the enzyme in the C4 dicarboxylic acid pathway of photosynthesis. Biochem. J. 112,549-558 (1969)... 

The transport of each COg requires the expenditure of two high-energy phosphate bonds. The energy of these bonds is expended in the phosphorylation of pyruvate to PEP (phosphoenolpyruvate) by the plant enzyme pyruvate-Pj dikinase the products are PEP, AMP, and pyrophosphate (PPi). This represents a unique phosphotransferase reaction in that both the /3- and y-phosphates of a single ATP are used to phosphorylate the two substrates, pyruvate and Pj. The reaction mechanism involves an enzyme phosphohistidine intermediate. The y-phosphate of ATP is transferred to Pj, whereas formation of E-His-P occurs by addition of the /3-phosphate from ATP ... 

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