Identification of a latent MAP kinase kinase kinase in PC12 cells as B‐raf

Abstract
A latent MAP kinase kinase kinase activity previously detected after chromatography of PC12 cell extracts on Mono Q [(1992) FEBS Lett. 314, 461–465] has been identified as B‐Raf by immunoblotting and immunoprecipitation experiments and by its specific activation with B‐Raf antibodies. B‐Raf is phosphorylated after stimulation of PC12 cells with nerve growth factor or epidermal growth factor, but this is not accompanied by activation of the Mono Q‐purified enzyme whether assayed in the absence or presence of GTP‐Ras.