Pre-incubation of subcellular fractions from rat cerebral cortex inactivates protein phosphorylation

Pre-incubation of various subcellular fractions from rat brain caused a significant decrease in the phosphorylation of individual polypeptides. The rate and extent of this loss of labelling was not uniform and polypeptides whose phosphorylation was independent of cyclic AMP were primarily affected, whereas substrate availability remained unaltered. It is recommended that pre-incubation effects must be carefully monitored if valid conclusions are to be made about the physiological relevance of changes in protein phosphorylation observed in vitro.