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Partial purification of a mitogen-activated protein kinase kinase activator from bovine brain. Identification as
A D Catling1, C W Reuter, M E Cox
1Department of Microbiology, University of Virginia Health Sciences Center, Charlottesville 22908.
Abstract:
A classical biochemical approach was taken to identify mitogen-activated protein kinase kinase (MEK) activators in bovine brain. Fractionation revealed the presence of one major MEK-stimulating activity that was distinct from c-Raf-1 and MEK kinase. Similar results were obtained using bovine adrenal chromaffin cells, and in both cases, immunoblotting and immunoprecipitation experiments demonstrated co-purification of MEK activator with B-Raf. Partially purified MEK activator stimulated phosphorylation of MEK1 on residues tentatively identified as serine 218 and serine 222. Little or no MEK activator was associated with c-Raf-1 in bovine brain or chromaffin cells, although this protein was expressed, suggesting that B-Raf might be the major MEK activator in cells of neural origin.