Identification of the 64 kilodalton chloroplast stromal phosphoprotein as phosphoglucomutase.

Phosphorylation of the 64 kilodalton stromal phosphoprotein by incubation of pea (Pisum sativum) chloroplast extracts with [gamma-(32)P]ATP decreased in the presence of Glc-6-P and Glc-1,6-P(2), but was stimulated by glucose. Two-dimensional gel electrophoresis following incubation of intact chloroplasts and stromal extracts with [gamma-(32)P]ATP, or incubation of stromal extracts and partially purified phosphoglucomutase (EC 2.7.5.1) with [(32)P]Glc-1-P showed that the identical 64 kilodalton polypeptide was labeled. A 62 kilodalton polypeptide was phosphorylated by incubation of tobacco (Nicotiana sylvestris) stromal extracts with either [gamma-(32)P]ATP or [(32)P]Glc-1-P. In contrast, an analogous polypeptide was not phosphorylated in extracts from a tobacco mutant deficient in plastid phosphoglucomutase activity. The results indicate that the 64 (or 62) kilodalton chloroplast stromal phosphoprotein is phosphoglucomutase.