Partial purification of a mitogen-activated protein kinase kinase activator from bovine brain. Identification as B-Raf or a B-Raf-associated activity.
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.
Department of Microbiology, University of Virginia Health Sciences Center, Charlottesville 22908.
A D
AD
Catling
C W
CW
Reuter
M E
ME
Cox
S J
SJ
Parsons
M J
MJ
Weber
D000311:Adrenal Glands / Q000201:enzymology / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002417:Cattle; D002478:Cells, Cultured; D002837:Chromaffin Granules / Q000201:enzymology / Q000378:metabolism; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D010766:Phosphorylation; D011233:Precipitin Tests; D011494:Protein Kinases / Q000302:isolation & purification*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf
D011518:Proto-Oncogene Proteins; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases