1. 1. A number of compounds from pathways associated with glucose and glycogen metabolism have been evaluated as regulators of the liver synthetase D phosphatase reaction. Although several were found to be inhibitory to the reaction, only ATP was an effective inhibitor at physiological concentrations. 2. 2. The inhibition by ATP was not a manifestation of either a stimulation of synthetase kinase or phosphoryllase kinase or the inhibition of phosphorylase phosphatase. All of these effects could result in an apparent inhibition of synthetase phosphatase. Whether the effect of ATP is on synthetase phosphatase or synthetase D, its substrate, is as yet unknown.
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The authors wish to thank Mrs Carol LaBresh for excellent technical assistance. This work was supported in part by a grant from the Twin Cities Diabetes Association.