Effect of growth at low temperature on the alternative pathway respiration in Acanthamoeba castellanii mitochondria

Mitochondria of amoeba Acanthamoeba castellanii in addition to the conventional cytochrome pathway possess, like plant mitochondria, a cyanide-resistant alternative quinol oxidase. In mitochondria isolated from amoeba batch culture grown tempo­rarily at low temperature (6°C), higher respiration was accompanied by lower cou­pling parameters as compared to control culture (grown at 28°C). In the presence of benzohydroxamate, respiratory rates and coupling parameters were similar in both types of mitochondria indicating that growth in cold conditions did not disturb the cytochrome pathway. Increased contribution of alternative oxidase in total mitochon­drial respiration in low-temperature-grown amoeba cells was confirmed by calcula­tion of its contribution using ADP/O measurements. Furthermore, in mitochondria from low-temperature- grown cells the content of the alternative oxidase was in­creased and correlated with the increase in the unstimulated and GMP-stimulated cya­nide-resistant respiratory activity. A possible physiological role of higher activity of alternative oxidase as response to growth at a low temperature in unicellular organ­isms, such as amoeba, is discussed.