Insulin‐induced decrease in 5′‐nucleotidase activity in skeletal muscle membranes

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Abstract
Insulin releases inositol phosphoglycans from myocytes in culture [(1986) Science 233, 967–972], which display insulinomimetic activity. Because 5′-nucleotidase is anchored to the membrane through inositol-containing phospholipid glycans, we investigated whether insulin could release the enzyme from the membrane. Membranes prepared from hindquarter muscles of rats perfused with insulin showed a 23% decrease in 5′-nucleotidase activity. Isolated membranes from muscle exposed to insulin in vitro also showed a small but reproducible decrease (9%) in 5′-nucleotidase activity relative to unexposed controls. Phospholipase C from Staphylococcus aureus released 60% of the membrane-bound 5′-nucleotidase. We propose that insulin may activate an endogenous phospholipase C that cleaves phospholipid-glycan-anchored proteins.