Stimulation of liver glycogen particle synthase D phosphatase activity by caffeine, AMP, and glucose 6-phosphate |
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Authors: | D P Gilboe F Q Nuttall |
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Affiliation: | 1. Endocrine Metabolic Section, Veterans Administration Medical Center, USA;1. Department of Biochemistry, University of Minnesota, Minneapolis, Minnesota 55417 USA;2. Department of Medicine, University of Minnesota, Minneapolis, Minnesota 55417 USA |
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Abstract: | Caffeine stimulates synthase and phosphorylase phosphatase activities by independent mechanisms. Both effects of caffeine are concentration-dependent with different apparent A0.5 for each reaction. Stimulation of the synthase phosphatase reaction was independent of the initial phosphorylase a concentration, was immediate, and did not follow in sequence the depletion of phosphorylase a. Glucose 6-phosphate also was stimulatory to the synthase phosphatase reaction (A0.5 = 0.14 mM) with little effect on phosphorylase phosphatase. In combination glucose 6-phosphate and caffeine effects were additive suggesting the existence of separate binding sites. The synthase phosphatase reaction also was stimulated by AMP (binding affinity 2.3 mm) but with no effect on phosphorylase phosphatase activity. Together caffeine and AMP effects were not additive suggesting that they share a common binding site or closely interrelated sites. The location of the AMP and caffeine site(s) has not yet been determined. |
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Keywords: | Address Correspondence to Daniel P. Gilboe VA Medical Center Endocrine Metabolic Section 54th St. and 48th Ave. S Minneapolis Minn. 55417. |
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