On the significance of adenylic acid aminohydrolase in skeletal muscle of vertebrates

Abstract

1. 1. The effect of AMP and IMP on the activity of phosphorylase b in the presence of the naturally occurring inhibitors ATP, ADP and glucose 6-phosphate has been re-investigated. 2. 2. In comparison with AMP, IMP is only a weak effector and its stimulating effect is completely abolished by the inhibitors. 3. 3. In the presence of either AMP or ADP plus adenylate kinase, the activity of phosphorylase b is abolished by the addition of AMP-aminohydrolase. These results are obtained in the presence of ATP at the “biological” concentration. 4. 4. If AMP-aminohydrolase were absent, the AMP formed during periods of muscle contraction would stimulate phosphorylase b to activity thus blunting the control of glycogenolysis exercised by the phosphorylase a to b interconversions. 5. 5. Considering the high concentrations of phosphorylase in skeletal muscle and the consequences of residual activity for glycogen preservation, one function of AMP-aminohydrolase is to control the level of AMP derived from the adenylate kinase reaction. 6. 6. The tail muscles of Cherax destructor have very little AMP-aminohydrolase and considerable amounts of adenylate kinase. Consequently, muscle contraction in the crustacean leads to the accumulation of AMP. 7. 7. During episodes of contraction, the stimulation of phosphofructokinase in invertebrates and vertebrates could be by AMP and ammonia respectively. In both cases, adenylate kinase acting on ADP would be the mediating step.