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.
MacDonald
Justin A
JA
Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada.
Storey
Kenneth B
KB
D000222:Adaptation, Physiological; D000818:Animals; D003080:Cold Temperature; D003600:Cytosol / Q000201:enzymology; D003681:Dehydration / Q000201:enzymology; D004795:Enzyme Stability; D005615:Freezing; D006003:Glycogen / Q000378:metabolism; D000860:Hypoxia / Q000201:enzymology; D007700:Kinetics; D018482:Muscle, Skeletal / Q000201:enzymology*; D009210:Myofibrils / Q000201:enzymology; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D011898:Ranidae / Q000502:physiology*; D013997:Time Factors
D006003:Glycogen; D010749:Phosphoprotein Phosphatases