Phosphorylation and dephosphorylation of hormone‐sensitive lipase Interactions between the regulatory and basal phosphorylation sites

Phosphorylation of the basal site with glycogen synthase kinase-4 enhanced the rate of phosphorylation of the regulatory site by cyclic AMP-dependent protein kinase 1.7-fold. In contrast, the phosphorylation state of the regulatory site did not affect the rate of phosphorylation of the basal site with glycogen synthase kinase-4. The rate of dephosphorylation of either the regulatory or the basal phosphorylation site by protein phosphatase-1, 2A or 2C was independent of the phosphorylation state of the other site. These results suggest that the basal phosphorylation site could play an indirect role in the control of the hormone-sensitive lipase activity in the adipocyte by functioning as a recognition site for the cyclic AMP-dependent protein kinase in the phosphorylation of the activity-controlling regulatory phosphorylation site in response to lipolytic hormones.