[Changes in phosphorylase activity during muscle alteration].

Changes in the extractability, and in the activity and ratios of active and inactive forms of phosphorylase (PhL) were studied under the action of heating and of urea on skeletal muscles of Rana temporaria L., and under the electric stimulation of the muscle. Besides, the action of these factors on the isolated enzyme was studied. Under the alteration of muscles due to heating, a decrease in extractability and in the activity of the whole PhL takes place. The isolated PhL is more thermostable than that in the intact muscle. Under the action of urea, a decrease in extractability and activity of the whole Phl occurs only with doses of urea which cause the irreversible alteration of muscle. In respect to urea stability, PhL in isolated state is one of the most labile enzymes of the water-soluble fraction. Under contractures produced by the action of heating and of urea, no transformation of an inactive PhL (PhL b) into the active PhL (PhL a) was revealed in the muscle. Under the tetanic contraction produced by the electric stimulation of muscle, a 2.5--3.0-fold increase of PhL a activity takes place under the invariable level of the whole PhL activity.