Deficiency in phosphorylase phosphatase activity despite elevated protein phosphatase type-1 catalytic subunit in skeletal muscle from insulin-resistant subjects.
Glycogen synthase is activated by protein phosphatase type-1 (PP-1). The spontaneous PP-1 activity accounts for only a small fraction of total PP-1 activity, which can be exposed by trypsin digestion of inhibitor proteins in the presence of Mn2+. We determined total PP-1 activity in muscle biopsies from insulin-sensitive and -resistant nondiabetic Pima Indians. Inhibitor-2 sensitive PP-1 represented 90% of total phosphatase activity. Spontaneous and total PP-1 activities were reduced in insulin resistant subjects (P less than 0.05-0.01), suggesting that the reduced PP-1 activity is not the result of inhibition by trypsin-labile phosphatase regulatory subunits. This difference was further investigated by Western blots using two different antibodies. An antibody raised against the rabbit muscle PP-1 catalytic subunit was used to analyze muscle extracts concentrated by DEAE-Sepharose adsorption. An antibody raised against a peptide derived from the COOH-terminal end of the PP-1 catalytic subunit was used to analyze crude muscle extracts. Both antibodies recognized a PP-1 catalytic subunit of approximately 33 kD, which unexpectedly was more abundant in insulin-resistant subjects (P less than 0.05-0.01). The increase in the tissue PP-1 protein content may be a response to compensate for the impairment in the enzyme activity.
Nyomba
B L
BL
Clinical Diabetes and Nutrition Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona 85016.
Brautigan
D L
DL
Schlender
K K
KK
Wang
W
W
Bogardus
C
C
Mott
D M
DM
D000328:Adult; D015153:Blotting, Western; D002384:Catalysis; D006006:Glycogen Synthase / Q000032:analysis; D006801:Humans; D007333:Insulin Resistance; D008345:Manganese / Q000494:pharmacology; D009132:Muscles / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000032:analysis*; D010765:Phosphorylase Phosphatase / Q000172:deficiency*; D014357:Trypsin / Q000494:pharmacology
D008345:Manganese; D006006:Glycogen Synthase; D010749:Phosphoprotein Phosphatases; D010765:Phosphorylase Phosphatase; D014357:Trypsin