Suppression of Na+K+ -ATPase activity by reversible phosphorylation over the winter in a freeze-tolerant insect.
Larvae of the gall fly, Eurosta solidaginis, use the cold hardiness strategy of freeze tolerance as well as entry into a hypometabolic state (diapause) to survive the winter. Cold hardiness strategies have been extensively explored in this species, but the metabolic features of winter hypometabolism have received little attention. A primary consumer of energy in cells is the ATP-dependent sodium-potassium ion pump (Na(+)K(+)-ATPase) so inhibitory controls over transmembrane ion movements could contribute substantially to energy savings over the winter months. Na(+)K(+)-ATPase activity was quantified in larvae sampled between October and April. Activity was high in October (0.56+/-0.13nmol/min/mg) but fell by 85% in November, remained low through midwinter, and then increased strongly in April. To determine whether the seasonal change in Na(+)K(+)-ATPase activity was linked with posttranslational modification of the enzyme, extracts from 15 degrees C-acclimated larvae were incubated under conditions that stimulated protein kinases A, G, or C. The action of all three kinases suppressed Na(+)K(+)-ATPase activity to levels just 3-8% of control values whereas the opposite treatment with alkaline phosphatase had no effect. Hence, the seasonal suppression of Na(+)K(+)-ATPase activity may be linked to enzyme phosphorylation. Furthermore, acute cold (3 degrees C) or hypoxia exposures of 15 degrees C-acclimated larvae did not alter enzyme activity, and freezing at -16 degrees C increased activity, so environmental factors do not appear to directly influence enzyme activity. Rather, it appears that winter suppression of ion motive ATPase activity may be part of a program of winter metabolic suppression.
McMullen
David C
DC
Department of Chemistry, Institute of Biochemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ont., Canada K1S 5B6. mcmulled@ninds@monds.ca
Storey
Kenneth B
KB
D000818:Animals; D003080:Cold Temperature; D007700:Kinetics; D007814:Larva / Q000201:enzymology; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism*; D012621:Seasons; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D033621:Tephritidae / Q000201:enzymology*
D010770:Phosphotransferases; D000254:Sodium-Potassium-Exchanging ATPase