MOLECULAR MECHANISMS OF INSULIN: GLYCOGEN SYNTHASE

The objective of these studies is to delineate the molecular
mechanism by which the phosphorylation state of skeletal muscle
glycogen synthase is altered in diabetes and by insulin treatment.
Emphasis will be focused on those protein kinases which
phosphorylate sites 2 and 3 in glycogen synthase and/or activate
the Mg++/ATP-dependent protein phosphatase I. Effects of the
insulin receptor tyrosine protein kinase on these serine/threonine
protein kinases and phosphatases will be examined directly using
purified enzymes as well as in situ in diaphragm and cultured
cells. In the latter case a highly specific antiphosphotyrosine
monoclonal antibody affinity column will be utilized to
selectively purify protein kinases and phosphatases containing
phosphotyrosine. Another approach will be to assess potential
effects of insulin-generated "modulator" molecules, derived from
a phosphatidylinositol-glycan by activation of a specific
phospholipase C, on these glycogen synthase protein kinases and
phosphatases. Potential effects of insulin on the subcellular
distribution of the protein kinase that activates the Mg /ATP-
dependent phosphatase and on the phosphatase itself will be
examined.