Separation of two phosphorylase kinase phosphatase activities in rabbit skeletal muscle

β Phosphorylase kinase phosphatase is the enzyme which reverses hormonal activation of phosphorylase kinase. The expression of its activity is dependent on the state of phosphorylation of the α subunit. α Phosphorylase kinase phosphatase can therefore be regarded as the enzyme which inhibits the reversal of the hormonal activation of phosphorylase kinase. The presence of separate enzymes in skeletal muscle specific for the dephosphorylation of each site implies that additional control mechanisms may well operate and the reversal of hormone stimulation may be under a very sophisticated form of control.