Trypsin-Mn(2+)-resistant form of type 1 protein phosphatase in human muscle.
Reduced type 1 protein phosphatase (PP-1) activity in human muscle extracts may contribute to the reduced insulin-stimulated glycogen synthase activity associated with insulin resistance for glucose disposal in humans. Because inactive forms of PP-1 can be activated with trypsin plus Mn2+, these reagents were used to compare the PP-1 activities in skeletal muscle extracts before and after separation into cytosolic and glycogen microsomal (GM) fractions. PP-1 activities were reduced in the GM fraction from insulin-resistant subjects (54 +/- 2 vs. 61 +/- 1, P < 0.01) but, in contrast to our previously published results, were elevated in the extract (33 +/- 6 vs. 18 +/- 3, P < 0.05). Recombination of the cytosol and GM fractions (reconstituted extract) demonstrated that the low extract PP-1 activities could only be regenerated when the GM fraction from insulin-sensitive subjects was recombined with cytosol from either group. The results indicate that the elevated PP-1 activity observed in extracts of insulin-resistant compared with insulin-sensitive subjects is caused by an inhibitor of extract PP-1 activity that sediments with the GM pellet and is more active in the insulin-sensitive subjects.
Mori
H
H
Clinical Diabetes and Nutrition Section, National Institutes of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona 85016.
Stone
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K
Mott
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DM
D000328:Adult; D003600:Cytosol / Q000378:metabolism; D004229:Dithiothreitol / Q000494:pharmacology; D004351:Drug Resistance; D005260:Female; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007333:Insulin Resistance; D008297:Male; D008345:Manganese / Q000494:pharmacology*; D008861:Microsomes / Q000378:metabolism; D009132:Muscles / Q000378:metabolism*; D009994:Osmolar Concentration; D010749:Phosphoprotein Phosphatases / Q000145:classification / Q000378:metabolism*; D014357:Trypsin / Q000494:pharmacology*
D008345:Manganese; D006003:Glycogen; D010749:Phosphoprotein Phosphatases; D014357:Trypsin; D004229:Dithiothreitol