Sequential activation of two mitogen activated protein (MAP) kinase isoforms in rat skeletal muscle following insulin injection.
Skeletal muscle is a major target of insulin action. The possible role of MAP kinase activation in insulin receptor signaling in muscle was examined. After a 48-hr fast, rats were injected intravenously with insulin or saline, muscles were excised after 3-20 min, homogenized, and MAP kinases were partially purified by ammonium sulfate precipitation and Mono Q chromatography. Activity was assayed as 32P-incorporation into myelin basic protein. Two activity peaks were identified; peak I eluted with approximately 0.1 M NaCl and peak II with approximately 0.2 M NaCl. Three min after insulin injection the activity of peak II increased > 2-fold, peak I was unchanged. After 10 min, the activity of peak II returned toward baseline, while peak I was activated approximately 3-fold. Immunoblots confirmed the presence of MAP kinases eluting with activity peaks I and II; the former as a approximately 41 kDa protein and the latter as a doublet of approximately 42 and approximately 44 kDa. The data suggest sequential activation of two MAP kinases in muscles; the isoform which activates/deactivates rapidly may represent ERK-1, while the more slowly responding isoform may be ERK-2.
Zhou
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GX
Department of Medicine, Medical University-of South Carolina, Charleston 29425-2222.
Meier
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KE
Buse
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MG
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D015151:Immunoblotting; D007328:Insulin / Q000494:pharmacology*; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008970:Molecular Weight; D009132:Muscles / Q000187:drug effects / Q000201:enzymology*; D010761:Phosphorus Radioisotopes; D051381:Rats; D017208:Rats, Wistar; D011972:Receptor, Insulin / Q000502:physiology; D015398:Signal Transduction
D007328:Insulin; D007527:Isoenzymes; D010761:Phosphorus Radioisotopes; D011972:Receptor, Insulin; D017871:Calcium-Calmodulin-Dependent Protein Kinases