The reoxidation of cytoplasmic reducing equivalents in Ehrlich ascites tumor cells

Abstract

1. Addition of glucose to ELD (Ehrlich-Lettre' hyperdiploid) ascites tumor cells inhibited by rotenone caused an oxidation-reduction cycle of cytochrome b and oxidation of cytochrome c but it did not affect the inhibition of the endogenous respiration. 2. The effect of substrates, inhibitors, and uncouplers of oxidative phosphorylation on the transition between the oxidized and the reduced steady state of cytochrome b induced by glucose in rotenone-inhibited cells was tested. The spectrophotometric data obtained support the hypothesis that this transition is determined by the initial lowering and the subsequent increase in the phosphate potential in the cytoplasmic compartment of the glycolyzing cell. 3. The reduction of cytochromes b and c induced by glucose in rotenone-inhibited cells in the presence of vitamin K 3 was shown to be biphasic. This reduction, like that produced by vitamin K 3 alone, was significantly increased by oligomycin or aurovertin, while the biphasicity of the response was no longer apparent with these inhibitors. 4. Pretreatment with pyruvate of rotenone-inhibited cells made it possible to show, upon addition of glucose, a rapid translocation ( t 1 2 about 700 msec) of reducing equivalents to a cytochrome b-type pigment with small or undetectable changes in the steady-state level of cytochrome c. This reaction, which may be tentatively assigned to the microsomal cytochrome b 5, was not competitive with the transfer of reducing equivalents to the mitochrondria in the presence of vitamin K 3. 5. It can be concluded that in the strain of ascites cells used no direct transport of reducing equivalents occurs under physiological conditions from the cytosol to the mitochondrial cytochromes. On the other hand a pathway for the extramitochondrial oxidation of the cytosolic reducing equivalents has been evidentiated.