Phosphorylation of the basal site of hormone‐sensitive lipase by glycogen synthase kinase‐4

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Abstract
In rat adipocytes hormone‐sensitive lipase is phosphorylated at two sites termed ‘regulatory’ and ‘basal’, in the former case by cyclic AMP‐dependent protein kinase causing an activation of the lipase [(1984) Proc. Natl. Acad. Sci. USA 81, 3317‐3321]. Here, the basal phosphorylation site was found to be phosphorylated by glycogen synthase kinase‐4 without any effects on lipase activity, or on the extent of its activation subsequent to phosphorylation of the regulatory site. Glycogen synthase kinase‐3, casein kinase‐I, and casein kinase‐II did not phosphorylate the lipase. Phosphorylase kinase phosphorylated it to a very low extent at a third phosphorylation site not phosphorylated in the fat cell.