IDENTIFICATION OF A B-50-LIKE PROTEIN IN FROG BRAIN SYNAPTOSOMES

Vestibular compensation in the frog following unilateral labyrinthectomy is accompanied by distinct changes in the endogenous phosphoprotein patterns in total frog brain homogenate and isolated synaptosomes. The purpose of this study was to characterize one of these proteins, an acidic 45-kDa synaptosomal protein, resembling in some of its features the growth-associated protein GAP-43/B-50. Our results demonstrate by comparative analysis with purified rat B-50/GAP-43 that the 45-kDa protein (IP 4.8) in synaptosomal membranes of frog brain is phosphorylated by added purified PKC, cross-reacts with affinity-purified rabbit antibodies to rat B-50 and exhibits a Staphylococcus aureus V8 protease peptide digestion pattern corresponding to rat B-50. Therefore, we conclude that the acidic 45-kDa synaptosomal protein is a growth-associated B-50-like protein, probably involved in processes responsible for compensatory reorganization of the vestibular structures after hemilabyrinthectomy in the frog.