Respiratory activities of liver mitochondria, isolated from freshwater turtle Chinemys revesii as an experimental anoxia-tolerant model system, determined by mitochondrial modifiers

Abstract

Abstract We isolated liver mitochondria from the anoxia-tolerant, Chinese three keeled pond freshwater turtle ( Chinemys revesii ). We found that the turtle liver mitochondria (TLM) had slow respiratory activities, which were dependent upon the amounts of complexes in respiratory chain, and H + /O and VH + /V H + leak ratios, induced by proton leakage. All of these values were lower than those of rat liver mitochondria (RLM). When mitochondrial modifiers, such as oligomycin and the uncoupler TX-109, were added to TLM, respiratory substrates such as isocitrate, 2-oxoglutarate, and malate were not significantly different between TLM and RLM. Respiration inhibition experiments showed that the enhanced rate of glutamate-dependent state 4 respiration in RLM was sixteen times faster than that in TLM, and other substrate-dependent state 4 respiration in RLM was eight times faster than that of TLM. We originally identified ubiquinone-10 (UQ-10) in TLM. In UQ-depleted TLM, the synthetic UQ analog idebenone at 0.1 mM restored the respiratory activity to a maximum of 12.8 natom O/min per mg protein, while in native TLM, idebenone at 0.4 mM restored the respiratory activity to a maximum of 26.2 natom O/min per mg protein. These results indicated that the low respiratory activities of TLM are attributed to their low substrate oxidation rate.