| Abstrakt: |
Oxidation of added NADH by rat liver mitochondria has been studied. It is found that exogenous NADH, when oxidized by rat liver mitochondria in sucrose hypotonic medium supplemented with Mg 2+and EGTA, generates a membrane potential (ΔΨ) even in the absence of added cytochrome c. ADP and phosphate decrease ΔΨ, the effect being reversed by oligomycin. Rotenone and myxothiazol do not inhibit ΔΨ generated by oxidation of exogenous NADH. Added cytochrome cincreases the rate of the exogenous NADH oxidation and coupled ΔΨ formation. In sucrose isotonic medium, or in hypotonic medium without Mg 2+, exogenous NADH fails to stimulate respiration and to form a membrane potential. In the presence of Mg 2+, exogenous NADH appears to be effective in ΔΨ generation in isotonic sucrose medium if mitochondria were treated with digitonin. In isotonic KCl without Mg 2+, oxidation of exogenous NADH is coupled to the ΔΨ formation and MgCl 2addition before mitochondria prevents this effect. In hypotonic (but not in isotonic) sucrose medium, Mg 2+makes a portion of the cytochrome cpool reducible by exogenous NADH or ascorbate. It is assumed that (i) hypotonic treatment or digitonin causes disruption of the outer mitochondrial membrane, and, as a consequence, desorption of the membrane-bound cytochrome cin a Mg 2+-dependent fashion; (ii) incubation in isotonic KCl without Mg 2+results in swelling of mitochondrial matrix, disruption of the outer membrane and cytochrome cdesorption whereas Mg 2+lowers the K +permeability of the inner membrane and, hence, prevents swelling; (iii) desorbed cytochrome cis reduced by added NADH via NADH-cytochrome b5reductase and cytochrome b5or by ascorbate and is oxidized by cytochrome oxidase. The role of desorbed cytochrome cin oxidation of superoxide and cytoplasmic NADH as well as possible relations of these events to apoptosis are discussed. |
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