Phosphopeptide and phosphoprotein metabolism in brain.

Phosphopeptide and phosphoprotein phosphorylation was studied in rat brain microsomes and rat brain slices which were incubated in the presence of [gamma-32 P] ATP under various experimental conditions. Radioactive phosphoserine was isolated from phosphopeptides and phosphoproteins. Naplus, K+, Mg2+ and cyclic AMP had a stimulating effect on the labelling of phosphopeptides. Ouabain and Ca2+ lowered the level of 32P incorporation into the phosphopeptides. The phosphoproteins behaved similarly to the phosphopeptides except for the potassium effect. Chase experiments showed a faster decrease in the labelling of phosphopeptides than in phosphoproteins. We suggest that both compounds may be involved in active transport phenomena.