Protein phosphatase type-1 from skeletal muscle of the freeze-tolerant wood frog.

We evaluated the effects of freezing, dehydration and anoxia stresses on muscle PP-1 activity in the freeze-tolerant amphibian, Rana sylvatica. In addition, PP-1 catalytic subunit (PP-1c) was purified to homogeneity to assess the biochemical properties of the enzyme from a freeze-tolerant vertebrate. Freezing stimulated a rise in the amount of active PP-1 (70% above the control) at 20 min post-nucleation. With longer freezing (1-12 h), the amount of active enzyme returned to control levels, and the amount of total PP-1 fell, decreasing by up to 43%. This decline in total PP-1 kept the % active at a high value throughout the freeze. Anoxia exposure (12 h) reduced the active PP-1 by 60%, but had no effect on total PP-1 activity. Neither dehydration nor rehydration had any significant effect on the amounts of either total or active PP-1. PP-1 activity associated with the myofibril fraction increased, while activity associated with the glycogen pellet decreased in response to freezing and dehydration, but not anoxia. Purified frog PP-1c showed a variety of properties that are typical of the enzyme from other sources. In addition, the enzyme was strongly inhibited by AMP and weakly by ADP and ATP; the physiological relevance of inhibition by nucleotides remains to be determined. Overall, the results suggest an important role for PP-1 in signal transduction in the skeletal muscle of freeze-tolerant amphibians.