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Journal of Lipid Research, Vol. 15, 602-610, November 1974
Copyright © 1974 by Lipid Research, Inc.

Reversible protein kinase activation of hormone-sensitive lipase from chicken adipose tissue

John C. Khoo and Daniel Steinberg

Division of Metabolic Disease, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, California 92037

Hormone-sensitive lipase partially purified from adipose tissue of laying hens was markedly activated by cyclic AMP-dependent protein kinase. Activation was approximately 4-fold (ranging up to as great as 10-fold) compared with the much lower degree of activation obtained with analogous preparations from rat and human adipose tissues (59 and 86%, respectively). The partially purified preparations contained adequate endogenous protein kinase activity to effect complete activation with addition of cyclic AMP, ATP, and Mg²⁺. Activation was blocked by protein kinase inhibitor (from rabbit skeletal muscle) but could be restored fully by addition of excess exogenous protein kinase (from bovine skeletal muscle). The fully activated lipase was slowly deactivated by dialysis at 4°C and then rapidly and almost fully reactivated by addition of cyclic AMP and ATP-Mg²⁺. Reactivation was blocked by protein kinase inhibitor. This deactivation-reactivation cycle was rapid at 23°C with dialysis against charcoal and could be demonstrated repeatedly using a single preparation. The reversible deactivation of protein kinase-activated enzyme is presumed to reflect the action of a lipase phosphatase. Lipase prepared from tissue previously exposed to glucagon yielded a much smaller degree of activation than lipase prepared from tissue not exposed to the lipolytic hormone, indicating that the physiological hormone-induced activation is probably similar to or identical with the protein kinase activation demonstrated in the cell-free preparations. Under the conditions of assay used, the partially purified lipase fraction contained diglyceride, monoglyceride, and lipoprotein lipase activities. However, treatment with cyclic AMP-dependent protein kinase had virtually no effect on these lipase activities.

Supplementary key words lipoprotein lipase • diglyceride lipase • monoglyceride lipase • glucagon • protein kinase inhibitor • cyclic AMP • lipase phosphatase

Submitted on June 5, 1974
Accepted on August 8, 1974

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