Phosphorylation of a stromal enzyme protein in maize zea mays cultivar kelvedon glory mesophyll chloroplasts

Foyer, C.

Biochemical Journal 222(1): 247-254


ISSN/ISBN: 0264-6021
Accession: 006107381

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When intact maize mesophyll chloroplasts were illuminated in the presence of polypeptide was a major component of the maize mesophyll chloroplast, comprising 10-15% of the total protein, which banded in an identical position to the apoprotein of the enzyme pyruvate, orthophosphate dikinase, which catalyzes a reaction of the C4 cycle. Phosphorylation in the 100 kDa species was prohibited by treatment of lysed chloroplasts with antibody to pyruvate, orthophosphate dikinase (EC The phosphorylated polypeptide observed after sodium dodecyl sulfate/polyacrylamide-gel electrophoresis is apparently the monomeric form of this enzyme. The 100 kDa polypeptide was partially phosphorylated in darkness, but a significant increase in the degree of phosphorylation was found on illumination. This polypeptide was dephosphorylated only slowly when the chloroplasts were returned to darkness. Maximum phosphorylation was observed in the presence of pyruvate or dihydroxyacetone phosphate, which also caused maximum activation of pyruvate, orthophosphate dikinase. Phosphorylation of the 100 kDa polypeptide did not coincide with deactivation of pyruvate, orthophosphate dikinase, but maximum phosphorylation occurred under conditions that promoted maximum activity of the enzyme, at which time 1 phosphate group was associated with each enzyme molecule. Protein phosphorylation did not appear to arise from the reaction mechanism of the enzyme.