THE ADDITION OF GLUCOSE-1-PHOSPHATE TO THE CYTOPLASMIC GLYCOPROTEIN PHOSPHOGLUCOMUTASE IS MODULATED BY INTRACELLULAR CALCIUM IN PC12 CELLS AND RAT CORTICAL SYNAPTOSOMES

In a number of different cell types, phosphorylation of a 63-kDa prote in has been shown to increase rapidly in response to stimuli that lead to an increase in intracellular calcium. Here, a stimulus-sensitive p rotein at this molecular weight is identified in PC12 cells and rat co rtical synaptosomes as phosphoglucomutase. In addition, the added phos phate is shown to be in an oligosaccharide terminating in phosphodiest er-linked glucose. In synaptosomes, incorporated radioactivity, follow ing incubation with [C-14]glucose or the [beta-S-35]phosphorothioate a nalogue of UDP-glucose, was found to increase within 5 s of stimulatio n and return to baseline within 25 s. Despite the many pathways utiliz ing glucose, this was the only detectable protein glycosylation observ ed in synaptosomes. These results indicate that cytoplasmic glycosylat ion is reversible and rapidly regulated, and suggest that phosphogluco mutase undergoes an alteration in function and/or topography in respon se to increases in intracellular calcium.