Regulation of C4 photosynthesis: identification of a catalytically important histidine residue and its role in the regulation of pyruvate,Pi dikinase |
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Authors: | J N Burnell M D Hatch |
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Affiliation: | CSIRO, Division of Plant Industry, GPO Box 1600, Canberra 2601, Australia |
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Abstract: | These studies provide further information regarding the mechanism of the light/dark-mediated regulation of pyruvate,Pi dikinase in leaves. It is shown that a catalysis-linked phosphorylation of pyruvate,Pi dikinase can be demonstrated following incubation of the enzyme with [32P]phosphoenolpyruvate or [beta-32P]ATP plus Pi, that the enzyme-bound phosphate is located on a histidine residue, and that this phosphate is retained during ADP-mediated inactivation. Further evidence is provided that phosphorylation of this histidine is a prerequisite for ADP-mediated inactivation through phosphorylation of a threonine residue from the beta-phosphate of ADP. It is demonstrated that diethylpyrocarbonate (which forms a derivative with histidine residues) prevents [32P]phosphoenolpyruvate-dependent labeling (catalytic labeling) and [beta-32P]ADP-dependent labeling (inactivation labeling) of the enzyme. In addition, it is demonstrated that oxalate, an analog of pyruvate, competitively inhibits ADP-dependent inactivation with respect to ADP. The significance of these results is discussed with regard to the mechanism of regulation of pyruvate,Pi dikinase in vivo. |
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Keywords: | To whom correspondence should be addressed. |
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