Effect of temperature on the activities of glucose-6-phosphate dehydrogenase and hexokinase in entomopathogenic nematodes (Nematoda: Steinernematidae)

Abstract

The kinetic properties of two metabolic enzymes, glucose-6-phosphate dehydrogenase and hexokinase, were studied in four strains of entomopathogenic nematodes that had been recycled for two years at various temperatures: Steinernema feltiae NF strain, Steinernema feltiae Umeå strain, Steinernema carpocapsae All strain, Steinernema riobravis TX strain. The recycling temperatures influenced the activities of glucose-6-phosphate dehydrogenase and hexokinase in an adaptive fashion in all the strains. At each assay temperature (5–35°C), the maximum specific activity of both the enzymes was greater in the nematodes that had been recycled at lower temperatures than in those reared at higher temperatures. In three enzyme-nematode strain combinations, the lowest K_m values measured at each assay temperature occurred in nematodes that had been recycled at the lower temperatures. However, the assay temperatures at which the minimum K_m values occurred were ≥15°C. The capacities of these nematodes to adjust to different recycling temperatures is discussed in relation to the physiological mechanisms involved.