Electron‐transfer restoration by vitamin K3 in a complex III‐deficient mutant of S. cerevisiae and sequence of the corresponding cytochrome b mutation

Abstract
The yeast box‐mutant W7 exhibits deficiencies in cytochrome b and in nuclear coded complex III subunits, a phenotype observed previously in a patient with mitochondrial myopathy. DNA sequence analysis of mutant W7 revealed a single base transition in the cytochrome b gene; the mutated residue Gly 131 is perfectly conserved in all known cytochromes b and belongs to the Q0 domain. Mutant W7 provides a model system for evaluating the action of therapeutic agents, such as vitamin K3 which restored NADH‐oxidase activity in the mutant as well as in the antimycin‐inhibited wild type. However, with the mutant, a greater quantity of menadione was necessary due to a decrease in other complex activities, and a much lower electron‐flow fraction passed through cytochrome oxidase.

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