• The Korean Journal of Pharmacology
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• v.27 no.2
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• pp.155-166
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• 1991

In order to evaluate a potential role of mitochondria in the mediation of toxicity of paraquat (PQ), submitochondrial particle and microsome of mouse liver were compared by oxygen radical generation and lipid peroxidation. With NADH in submitochondrial particle and NADPH in microsome as electron donors, PQ stimulated production of superoxide anion and $H_2O_2$ in both fractions. Under the same conditions, PQ enhanced the generation of ethylene from methional suggestiong stimulation of OH production by PQ. But these effects by PQ were somewhat lower in submitochondrial particle than in microsome. In addition, lipid peroxidation(measured as MDA production) was stimulated by PQ in both fractions. The stimulation of lipid peroxidation in both fractions seemed to occur by the same mechanism probably through perferryl ion. This was supported by the following findings: i) The lipid peroxidation in both fractions was partially inhibited by SOD and completely inhibited by DETAPAC(an iron chelator) but not by catalase or OH scavenger. ii) Addition of $ADP-Fe^{3+}$ further increased PQ-induced lipid peroxidation but decreased ethylene production from methional suggesting no correlation between OH production and lipid peroxidation. The redox-cycling of PQ in mitochondria appeared to be linked to NADH dehydrogenase, not to CoQ since all of the observed stimulations by PQ in submitochondrial particle were inhibited by p-hydroxymercuribenzoate(a NADH dehydrogenase inhibitor) but not affected by other respiratory chain blockers. The above results demonstrate that redox-cycling properties of PQ leading to oxygen radical generation and lipid peroxidation can also occur in mitochondria in the same manner as in microsome. Therefore, the observed actions of PQ in mitochondria suggest that mitochondria may also contribute to toxicity of this drug in vivo.

• Applied Biological Chemistry
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• v.28 no.4
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• pp.271-277
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• 1985

A polarograph with specially designed cell compartment usable in kinetic study of the mitochondrial respiration of a small sized sample was made, and its performance and experimental conditions were examined. An applied potential (ca-1.2V vs. SCE) which gives rise to the second step reduction of oxygen caused a considerable level of a residual current independent of oxygen, which is temporarily interpreted as the reduction current of the membrane-bound redox material(s) of mitochondria. A potential corresponding to the first slop reduction of oxygen (ca-0.4V vs SCE) did not produce the residual current. Thus, it is suggested that a measurement of oxygen concentration in a sample of mitochondria and submitochondrial particles by using dropping mercury electrode should be done with an applied potential of about -0.4V vs SCE. Consumption of oxygen by mitochondria was observed to follow practically zero order kinetics. Its rate constant exhibited the proportional relationship with the respiratory activity of mitochondria. Usefulness of tile instrument was properly demonstrated in the work on the temperature effect on the respiration of mitochondria isolated from several plant 4issues which were selected on the basis of chilling susceptivity.

• Applied Biological Chemistry
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• v.32 no.1
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• pp.23-29
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• 1989

Biochemical consequence of the accumulation in cells of superoxide $(O^{-}_{2})$ which was proposed to be probably a common chemical factor in the secondary process of the mechanism of chilling injury as well as in the visible light photodamage in cells of higher plants, has been investigated in the present work. Especially focused was the destructive effect of $O^{-}_{2}$ on the biochemical activity of mitochondria, as informations which support the suggestion that mitochondrial inner membrane is the major site of $O^{-}_{2}$ production have been collected. Mitochondria and submitochondrial particles (SMP) were prepared from soybean hypocotyls for this case study. When SMP were treated with the electrolytically produced $O^{-}_{2}$ they suffered not only inhibition of the membrane-bound enzymes as demonstrated by cytochrome c oxidase, but also lipid peroxidation of membrane as proved by malondialdehyde production. Malate dehydrogenase present in the protein extract from mitochondrial matrix was also inhibited by the $O^{-}_{2}$ treatment. These results exhibited the chaotic effect of the overproduction and accumulation of $O^{-}_{2}$ in cells under a certain abnormal circumstance such as environmental stress on the physiological function of mitochondrial; disruption of the cellular metabolic pathways and the structural integrity of membrane.