The effects of seasonal change, November versus July, and prolonged
anoxia (96 h under N2 gas) on the properties of
phosphofructokinase and
pyruvate kinase from five tissues (gill, mantle, hepatopancreas, phasic adductor, catch adductor) of the oyster, Crassostrea virginica were investigated. Both
enzymes showed tissue-specific and season-specific changes in kinetic properties; for
pyruvate kinase this correlated with seasonal differences in
enzyme elution patterns on
hydroxylapatite chromatography. Kinetic properties of both
enzymes in winter were consistent with primarily catabolic roles in glycolysis with responsiveness to cellular energy demands, whereas in summer these
enzymes may be more closely regulated with respect to the biosynthetic 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
hydroxylapatite in all tissues except mantle, with much greater effects seen for the
enzyme from winter versus summer animals. For example,
anoxia-induced changes in
pyruvate kinase from winter gill included a fourfold rise in the substrate 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 activity by 50%. Changes in
pyruvate kinase kinetics and
hydroxylapatite elution patterns during prolonged
anoxia are consistent with covalent modification of
pyruvate kinase but contrary to results for many other mollusc species,
anoxia exposure appears to induce a dephosphorylation of the
enzyme.