Seasonal change and prolonged anoxia affect the kinetic properties of phosphofructokinase and pyruvate kinase in oysters

The effects of seasonal change, November versus July, and prolonged anoxia (96 h under N-2 gas) on the properties of phosphofructokinase and pyruvate kinase from five tissues (gill, mantle, hepatopancreas, phasic adductor. ca tch adductor) of the oyster, Crassostrea virginica, were investigated. Both enzymes showed tissue-specific and season-specific changes in kinetic prop erties: for pyruvate kinase this correlated with seasonal differences in en zyme elution patterns on hydroxylapatite chromatography. Kinetic properties of both enzymes in winter were consistent with primarily catabolic roles i n glycolysis with responsiveness to cellular energy demands, whereas in sum mer those enzymes may be more closely regulated with respect to the biosynt hetic and gluconeogenic functions of the tissues. Anoxia-induced changes in phosphofructokinase properties were relatively minor but anoxia stimulated changes in pyruvate kinase properties and elution profiles on hydroxylapat ite in all tissues except mantle, with much greater effects seen for the en zyme from winter versus summer animals. For example, anoxia-induced changes in pyruvate kinase from winter gill included a fourfold rise in the substr ate affinity constant for phosphoenolpyruvate, a sevenfold increase in the concentration of fructose-1,6-bisphosphate needed to activate the enzyme by 50%, and a 50% decrease in the concentration of L-alanine that inhibits ac tivity by 50%. Changes in pyruvate kinase kinetics and hydroxylapatite elut ion patterns during prolonged anoxia are consistent with covalent modificat ion of pyruvate kinase but contrary to results for many other mollusc speci es, anoxia exposure appears to induce a dephosphorylation of the enzyme.