THERMAL REGULATION OF ACTIVE OXYGEN-SCAVENGING ENZYMES IN CRITHIDIA-LUCILIAE THERMOPHILA

The insect hemoflagellate Crithidia luciliae thermophila can be mainta ined in culture within a range of temperatures from 15 to 37 C. In an attempt to determine the biochemical basis of its unusual thermal tole rance, we measured the specific activities of active oxygen-scavenging enzymes in C. luciliae thermophila maintained at 25 C and at 37 C. Hy perthermia is associated with an 82% increase in the specific activity of superoxide dismutase without a qualitative change in the spectrum of isoenzymes, a 54% decrease in catalase, and a 34% increase in NADPH -dependent hydrogen peroxide consumption. Our results suggest that the superoxide dismutase present in C. luciliae thermophila is an iron-co ntaining superoxide dismutase and that increased superoxide-scavenging ability accounts in part for survival at elevated temperatures. In th e related trypanosomes and leishmanias, active oxygen scavenging contr ibutes to the capacity to withstand oxidant-mediated phagocyte killing and resistance to some anti-parasitic drugs. The thermotolerance of C . luciliae thermophila recommends it as a model for investigating heat -induced gene expression in relation to parasite survival.