Protein kinase and phosphatase responses to anoxia in crayfish, Orconectes virilis: purification and characterization of cAMP-dependent protein kinase
2001
Cowan, K.J. | Storey, K.B.
The freshwater crayfish, Orconectes virilis, shows good anoxia tolerance, enduring 20 h in N2-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 N2-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 (Km = 131.0 +/- 14.4 micromolar) and Kemptide (Km = 31.6 +/- 5.2 micromolar). 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.
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