Kinetic and regulatory properties of pyruvate kinase from Artemia embryos during incubation under aerobic and anoxic conditions. The effect of pH on the kinetic constants

PK from Artemia embryos displayed sigmoidal kinetics with respect to phosphoenolpyruvate while saturation curves for ADP followed regular hyperbolas. The enzyme was strongly affected by ATP, alanine and fructose 1,6-bisphosphate, the latter increasing the affinity for PEP up to 10-fold. In order to assess whether Artemia PK is regulated by covalent modification, kinetic parameters were determined at various stages of development as well as after exposure of Artemia embryos to anoxic conditions. Incubation under anoxic conditions had no strong effect on the kinetic parameters of the enzyme. In addition, only a small effect of pH changing on the PK kinetic constants was observed. The results of the present study provide no evidence to suggest that Artemia PK is covalently modified in response to anoxia. Therefore, it appears that alternative mechanisms are involved in the depression of metabolic rate observed during the transition of Artemia embryos into anaerobic dormancy.