| 210759 |
Halestrap AP: Stimulation of the respiratory chain of rat liver mitochondria between cytochrome c1 and cytochrome c by glucagon treatment of rats. Biochem J. 1978 Jun 15;172(3):399-405.
Mitochondria from glucagon-treated rats oxidize succinate, but not ascorbate plus tetramethylphenylenediamine, faster in the uncoupled state than do control mitochondria. The rate of O (2) uptake in the presence of both substrates is equal to the sum of the rates of the O (2) uptake in the presence of either substrate alone. It is concluded that the mitochondrial respiratory chain is limited at some point between cytochromes b and c and that this step is regulated by glucagon. Measurement of the cytochrome spectra under uncoupled conditions in the presence of succinate and rotenone demonstrates a crossover between cytochromes c and c (1) when control mitochondria are compared with those from glucagon-treated rats, cytochrome c being more oxidized and cytochrome c (1) more reduced in control mitochondria. Under conditions where pyruvate metabolism is studied the control mitochondria are generally more oxidized than those from glucagon-treated rats, the redox state of cytochrome b-566 correlating with the rate of pyruvate metabolism in sucrose medium. However, when the redox state of the mitochondria is taken into account, a crossover between cytochromes c and c (1) is again apparent. The spectra of the b cytochromes are complex, but cytochrome b-562 appears to become more reduced relative to cytochrome b-566 in mitochondria from glucagon-treated rats than in control mitochondria. This can be explained by the existence of a more alkaline matrix in glucagon-treated rats, the redox potential for cytochrome b being pH-sensitive. It is concluded that glucagon stimulates electron flow between cytochromes c (1) and c. The physiological significance of these findings is discussed. |
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