High levels of a heat-labile calmodulin-binding protein (CaM-BP80) in bovine neostriatum

Bovine brain contains a heat-labile, 80,000-dalton calmodulin-binding protein (CaM-BP80) which inhibits the calmodulin-dependent activities of cyclic 3',5'-nucleotide phosphodiesterase, adenylate cyclase, and Ca2+-ATPase in vitro. CaM-BP80 is composed of two polypeptides (60,000 and 18,500 daltons) present in a 1:1 ratio. An antibody directed against CaM-BP80 was raised in rabbits, and a radioimmunoassay was developed, having a sensitivity of 60 fmol of CaM-BP80. Using the radioimmunoassay, we determined the levels of CaM-BP80 in various bovine tissues. The protein was found primarily in the brain, present in particularly high levels in the neostriatum. These results, together with immunohistochemical localization of CaM-BP80 at the postsynaptic densities and the microtubules of postsynaptic dendrites [Wood, J.G., Wallace, R., Whitaker, J., & Cheung, W.Y. (1980) J. Cell Biol. 84, 66-76], suggest that the protein may have a role in the cerebrum at the site of neurotransmitter action and at the level of microtubular function.