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Insulin stimulates the activity of mitogen-activated protein kinase (MAPK) via its upstream activator, MAPK kinase (MEK), a dual specificity kinase that phosphorylates MAPK on threonine and tyrosine. The potential role of MAPK activation in insulin action was investigated with the specific MEK inhibitor PD98059. Insulin stimulation of MAPK activity in(More)
The preparation of a number of agarose and polyacrylamide bead derivatives useful in the purification of proteins by afhnity chromatography is described. These techniques permit (a) the attachment of ligands to the gel through extended hydrocarbon chains which place the ligand at varying distances from the gel matrix backbone; (b) the covalent attachment of(More)
The purification of proteins by conventional procedures is frequently laborious and incomplete, and the yields are often low. Enzyme isolation based on a highly specific biological property-strong reversible association with specific substrates or inhibitors-has received only limited attention.‘-’ In affinity chromatography, the enzyme to be purified is(More)
Tumor necrosis factor (TNF) is a proteinaceous toxin shed by stimulated myeloid cells. Murine TNF was radioiodinated to a specific activity of 1 mCi/nmol (1 Ci = 37 GBq) of monomer. 125I-labeled TNF (125I-TNF) retained complete cytotoxic activity and it was immunochemically identical to the native toxin in a quantitative immunoprecipitation assay. It could(More)
A spectrophotometric assay is described for staphylococcal nuclease, based on the increase in absorbance at 260 mp which accompanies deoxyribonucleic acid and RNA hydrolysis. Initial velocities are proportional to enzyme concentration over a 70-fold range. The enzyme has greater aflinity for DNA than for RNA, and activity is greater with heat-denatured DNA(More)
An assay system is described for measurement of specific binding of [(125)I]insulin to intact fat cells and membrane fractions from such cells. The binding is time- and temperature-dependent and saturable with respect to insulin; the bound insulin is displaced by native insulin but not by oxidized or reduced insulin or by a number of other peptide hormones.(More)