Phosphorylation of Superior Cervical Ganglion Proteins During Regeneration

Abstract: The incorporation of radioactive phosphate into proteins of both normal and regenerating ganglia of the sympathetic nervous system of the rat is reported. The incorporation reactions were carried out in vitro by incubating homogenates of excised ganglia with [γ‐³²P]ATP under various conditions. It was found that incorporation of phosphate into proteins of regenerating ganglia in the molecular mass range 10,000–100,000 daltons increased up to 40% over incorporation into proteins from control ganglia during the first 3 days following injury and returned to control levels after 14 days. Analysis of the proteins by two‐dimensional electrophoresis revealed that only few, i.e., <20, became radioactively labelled in homogenates of superior cervical ganglia in the presence of Ca²⁺, and even fewer in the presence of cyclic AMP. Furthermore, all these proteins fell within a narrow pI range of 4–6. The growth‐associated protein, variously designated GAP‐43, B‐50, F‐1, and pp46, has an enhanced level of expression and phosphorylation in regenerating ganglia compared with controls at day 3. Injury also caused consistently higher levels of incorporation into two other proteins with molecular masses at positions 55,000 and 85,000 and pI values of 5.1 and 4.5, respectively; the former protein most probably is β‐tubulin. The fact that both proteins are found in the 15,000 g pellet after the tissue has been solubilized in 0.5% nonionic detergent indicates that they may indeed be components of filament assemblies. Thus, the results suggest that protein phosphorylation is a mechanism involved in cytoskeletal function in regenerating nerve.