Multiple forms of cyclic nucleotide phosphodiesterases in normal and goitrous rat thyroid |
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Authors: | R V Sharma R C Bhalla |
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Institution: | Department of Physiological Chemistry, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205 U.S.A. |
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Abstract: | The stoichiometry of H+ ejection coupled to electron flow from succinate to ferricyanide in the electron transport chain of mitochondria from Ehrlich ascites tumor and AS30-D hepatoma cells was determined. Values close to 4.0 for the ejection ratio were found in both cell lines, with either Ca2+ or K+ (+ valinomycin) as charge-compensating permeant cation. The 4 H+ ejected were compensated by outward movement of two negative charges to reduce 2 Fe(CN)63? to 2 Fe(CN)64?, and the uptake of two positive charges in the form of the permeant cation. Experiments on (a) omission of rotenone (b) the effect of antimycin A and (c) depletion of endogenous NAD(P)-linked substrates showed that no significant endogenous electron flow or H+ ejection occurred, thus eliminating possible overestimation of the H+/2e? ratio from endogenous substrates. These data on mitochondria from two tumor cell lines are fully consistent with earlier measurements of the H+/O stoichiometry for succinate and NADH oxidation in tumor mitochondria and with the stoichiometry for site 2 in normal rat liver mitochondria. |
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