AJP - Endocrinology and Metabolism, Vol 266, Issue 4 E574-E582, Copyright © 1994 by American Physiological Society
Trypsin-Mn(2+)-resistant form of type 1 protein phosphatase in human muscle
H. Mori, K. Stone and D. M. Mott
Clinical Diabetes and Nutrition Section, National Institutes of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona 85016.
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.
