The temperature dependence of the response to valinomycin and gramicidin by isolated liver mitochondria from warm- and cold-blooded animals

Abstract

1. 1. Arrhenius plots of the increase in oxygen uptake by rat or mouse liver mitochondria following a sub-maximal dose of gramicidin D or valinomycin show clear-cut inflections at about 16°C. 2. 2. With the mammalian preparations activation energies above the inflection are low for gramicidin but significantly higher for valinomycin. Over the lower part of the range gramicidin shows greater temperature dependence than valinomycin. There is no indication of a non-intersecting discontinuity in the response to valinomycin at the transition temperature. 3. 3. Arrhenius plots for rainbow trout liver mitochondria are linear over the whole experimental temperature range (5–30°C) for both antibiotics. The activation energy for gramicidin is significantly greater than that for valinomycin. 4. 4. These results are discussed in relation to other work on phase transitions in artificial lipid systems and the temperature dependence of membrane-bound enzyme activities. 5. 5. The possible effect of configurational changes in the mitochondrial membranes is considered in conjunction with the differing modes of action of these two antibiotics.