1. 1. The effect of glucose, caffeine, AMP and polyamines was investigated on the dephosphorylation of phosphorylase a by the catalytic subunits of protein phosphatase-1 and -2A. 2. 2. Caffeine at 1-20 μM inhibited the dephosphorylation of the dimeric phosphorylase a at 37°C using skeletal muscle enzymes; 0.1-10 mM of caffeine enhanced the rate of dephosphorylation greatly at 13°C and slightly at 37°C. 3. 3. α-d-Glucose was more effective in accelerating both the dephosphorylation and the tryptic digestion of phosphorylase a than the β-anomer. 4. 4. Polyamines were found to moderate the inhibitory effect of AMP at concentrations which may occur in the tissues. In the presence of 5 mM glucose polyamines could cancel the AMP inhibition of the dephosphorylation of liver phosphorylase a by hepatic protein phosphatase-1 and -2A.
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