ACTH1--24 releases a protein from synaptosomal plasma membranes

Brain membranes contain several protein kinases, all of which appear to play a role in the regulation of neuronal functioning. These membranes also contain numerous (phospho) proteins. It has been proposed that the degree of phosphorylation of some of these proteins may affect neuronal membrane properties. In a series of previous reports we showed that ACTH1--24 inhibits the endogenous phosphorylation of several synaptosomal plasma membrane (SPM) proteins including the B-50 protein. Although we have speculated that the degree of phosphorylation of B-50 may be important in regulating the turnover of membrane (poly)-phosphoinositides, the exact nature of the interaction between ACTH1--24 and B-50/B-50 protein kinase is unknown. The purpose of the present study was to determine whether treatment of SPM with ACTH1--24 will lead to a specific release of proteins from SPM. We found that ACTH1--24 specifically releases a 41,000 Mr protein from rat brain SPM. Although we are not certain about the biological significance of the release of this polypeptide, it is of sufficient interest for further research in view of the lack of success of finding binding of labeled ACTh to brain membranes.