Mitochondrial adenosine triphosphatase activity and temperature adaptation inSchistocephalus solidus(Cestoda: Pseudophyllidea)

Abstract

SUMMARYDuring its life-cycle, the cestodeSchistocephalus solidusis parasitic in both an ectotherm (Gasterosteus aculeatus) and an endotherm (Gallus domesticus) host, and so provides an excellent model with which to study temperature adaptation in parasites. A mitochondrial fraction was prepared from the adults and plerocercoids ofS. solidusand from their respective hosts; the activities of the mitochondrial adenosine triphosphatase (ATPase) were then measured over the temperature range 1–45 °C. The plerocercoids ofS. solidusshow evidence of immediate temperature compensation; this would provide a mechanism for withstanding the abrupt temperature change experienced during infection of the final host. Analysis of the Michaelis constant data suggests that variation of Km, awith temperature may be a major factor in this immediate temperature compensation. In response to acclimation at 5 and 19°C, plerocercoid ATPase showed inverse or paradoxical rate compensation, as did the enzyme from the fish host. Acclimation at the two temperatures had no effect on the Q10or on the linearity of the Arrhenius plots for the plerocercoid mitochondrial ATPase and only a small effect on the Km a. Acclimation of the fish host again had only a small effect on the Km, aof the fish mitochondrial ATPase but, in contrast to the plerocercoid, there was also a significant effect on the Q10and the Arrhenius plots. AdultS. solidusATPase showed partial rate compensation and had a biphasic Arrhenius plot, suggesting that after infection there had been a change in the enzyme or its micro-environment. In terms of the effect of temperature on the Q10amd Km, aand in the biphasic nature of the Arrhenius plot, the mitochondrial ATPase of adultS. solidusshowed similarities with the enzyme from its bird host.