Regulation of C4 photosynthesis: purification and properties of the protein catalyzing ADP-mediated inactivation and Pi-mediated activation of pyruvate, Pi dikinase
Burnell, J.N., and Hatch, M.D. (1985) Regulation of C4 photosynthesis: purification and properties of the protein catalyzing ADP-mediated inactivation and Pi-mediated activation of pyruvate, Pi dikinase. Archives of Biochemistry and Biophysics, 237 (2). pp. 490-503.
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Pyruvate,Pi dikinase regulatory protein (PDRP) has been highly purified from maize leaves, and its role in catalyzing both ADP-mediated inactivation (due to phosphorylation of a threonine residue) and Pi-mediated activation (due to dephosphorylation by phosphorolysis) of pyruvate,Pi dikinase has been confirmed. These reactions account for the dark/light-mediated regulation of pyruvate,Pi dikinase observed in the leaves of C4 plants. During purification to apparent homogeneity the ratio of these two activities remained constant. The molecular weight of the native PDRP was about 180,000 at pH 8.3 and 90,000 at pH 7.5. Its monomeric molecular weight was 45,000. It was confirmed that inactive pyruvate,Pi dikinase free of a phosphate group on a catalytic histidine was the preferred substrate for activation. Michaelis constants for orthophosphate and the above form of active pyruvate,Pi dikinase were determined, as well as the mechanism of inhibition of the PDRP-catalyzed reaction by ATP, ADP, AMP, and PPi. For the inactivation reaction, Km values were 1.2 microM for the active pyruvate,Pi dikinase and 52 microM for ADP. CDP and GDP but not UDP could substitute for ADP. The inactivation reaction is inhibited by inactive pyruvate,Pi dikinase competitively with respect to both active pyruvate,Pi dikinase and ADP. Both the activation and inactivation reactions catalyzed by PDRP have a broad pH optimum between 7.8 and 8.3. The results are discussed in terms of the likely mechanism of dark/light regulation of pyruvate,Pi dikinase in vivo.
|Item Type:||Article (Refereed Research - C1)|
|FoR Codes:||06 BIOLOGICAL SCIENCES > 0601 Biochemistry and Cell Biology > 060104 Cell Metabolism @ 100%|
|SEO Codes:||97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%|
|Deposited On:||12 Nov 2010 14:06|
|Last Modified:||12 Feb 2011 03:54|
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