抄録
The inhibitors of cytochrome oxidase [EC 1. 9. 3. 1] so far examined were classified into three groups based on their modes of action which were kinetically analyzed. One molecule of cytochrome a combines with one molecule of either cyanide, azide or sodium bisulfite, and with two molecules of either fluoride, hydroxylamine, hydrazine, semicarbazide, ethylxanthate, salicylaldoxime or EDTA. Any one of these cytochrome a-inhibitor complexes except those with fluoride and hydroxylamine is completely inactive. In the latter case, a 1:1 cytochrome a-inhibitor complex still retains some residual activity whereas a 1:2 complex is completely inactive. A cooperative interaction between two binding sites on cytochrome a was suggested for the inhibitors, except for NH2OH with which cytochrome a formed 1:2 com-plexes. The association-dissociation phenomenon of cytochrome a molecules seemingly was not responsible for several types of inhibitions so far observed, and the validity of the inhibition mechanism proposed was discussed in detail.
2. An apparent enhancement of the inhibition during the oxidation of ferrocyto-chrome c, which was catalyzed by cytochrome a in the presence of either one of the above inhibitors other than EDTA, was suggested to be due to a progressive formation of a cytochrome a-inhibitor complex. A transient alteration of cytochrome a molecules prior to the complex formation was also suggested from kinetic analyses of the inhibition data.
