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Phosphorylation of pea chloroplast acetyl-CoA carboxylase

Savage, L.J., Ohlrogge, J.B.
The plant journal 1999 v.18 no.5 pp. 521-527
Pisum sativum, chloroplasts, acetyl-CoA carboxylase, phosphorylation, adenosine triphosphate, amino acid sequences, molecular conformation, isotope labeling, light, enzyme activity, phosphoproteins
We have examined whether chloroplast acetyl-CoA carboxylase is a phosphoprotein. Pea (Pisum sativum) chloroplasts were incubated in the presence of [gamma-(33)P]- ATP and radiolabeled proteins were examined after immunoprecipitation with antibodies against all four known subunits of heteromeric chloroplast acetyl-CoA carboxylase. The beta-subunit of the carboxyltransferase was found to be labeled by (33)P. Phosphoamino acid analysis of the immunoprecipitated beta-subunit of the carboxyltransferase indicates that it is phosphorylated on serine residues. Incorporation of (33)P into carboxyltransferase beta-subunit decreased in chloroplasts transferred to dark conditions after labeling in the light. Dephosphorylation of pea chloroplast extracts by an alkaline phosphatase-agarose conjugate reduced in vitro acetyl-CoA carboxylase activity by 67%. Furthermore, while acetyl-CoA carboxylase activity and its carboxyltransferase half-reaction were reduced in dephosphorylated extracts, the biotin carboxylase half reaction was not inhibited. The evidence presented here points to the carboxyltransferase beta-subunit of chloroplast acetyl-CoA carboxylase as a candidate for regulation by protein phosphorylation/dephosphorylation.