title: Protein kinase and phosphatase responses to anoxia in crayfish, Orconectes virilis: purification and characterization of cAMP-dependent protein kinase.
abstract: The freshwater crayfish, Orconectes virilis, shows good anoxia tolerance, enduring 20 h in N(2)-bubbled water at 15 degrees C. Metabolic responses to anoxia by tolerant species often include reversible phosphorylation control over selected enzymes. To analyze the role of serine/threonine kinases and phosphatases in signal transduction during anoxia in O. virilis, changes in the activities of cAMP-dependent protein kinase (PKA) and protein phosphatases 1, 2A, and 2C were measured in tail muscle and hepatopancreas over a time course of exposure to N(2)-bubbled water. A strong increase in the percentage of PKA present as the free catalytic subunit (% PKAc) occurred between 1 and 2 h of anoxia exposure whereas phosphatase activities were strongly reduced. This suggests that PKA-mediated events are important in the initial response by tissues to declining oxygen availability. As oxygen deprivation became severe and prolonged (5-20 h) these changes reversed; the % PKAc fell to below control values and activities of phosphatases returned to or rose above control values. Subcellular fractionation also showed a decrease in PKA associated with the plasma membrane after 20 h anoxia whereas cytosolic PKA content increased. PKAc purified from tail muscle showed a molecular weight of 43.8+/-0.4 kDa, a pH optimum of 6.8, a high affinity for Mg ATP (K(m)=131.0+/-14.4 microM) and Kemptide (K(m)=31.6+/-5.2 microM). Crayfish PKAc was sensitive to temperature change; a break in the Arrhenius plot occurred at approximately 15 degrees C with a 2.5-fold rise in activation energy at temperatures <15 degrees C. These studies demonstrate a role for serine/threonine protein kinases and phosphatases in the metabolic adjustments to oxygen depletion by crayfish organs.
authors.affiliation: Institute of Biochemistry and Department of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6.
authors.forename: K J
authors.initials: KJ
authors.lastname: Cowan
authors.forename: K B
authors.initials: KB
authors.lastname: Storey
mesh_terms: D000818:Animals; D003400:Astacoidea; D002384:Catalysis; D002850:Chromatography, Gel; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism*; D004064:Digestive System / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia; D007700:Kinetics; D009132:Muscles / Q000201:enzymology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
chemical_list: D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases