Effect of pH on inhibition of cyanide-resistant respiration by hydroxamic acids inRhodotorula glutinis
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The extent of inhibition of cyanide-insensitive respiration inRhodotorula glutinis by salicylhydroxamic (SHAM) and bezhydroxamic acid depends on the pH of the cell suspension; maximum inhibition occurs at pH 4–6, at higher pH values the inhibitory capacity Tapidly drops. The acidity of the medium affects primarily the degree of dissociation of hydroxamic acids which, as weak acids, pass through the yeast cell membrane only as neutral molecules (Kotyk 1963; de la Peánaet al. 1982). In a medium more alkaline than the cell interior the fraction of the acids distributed into the cell decreases and a full inhibition requires an increased concentration of the acid in the medium. Cyanide-resistant respiration was also found inSaccharomyces cerevisiae; even here medium alkalinization eliminates the inhibitory effect of hydroxamic acids but, in contrast toR. glutinis, the cell membrane is permeable also to 2-iodobenzhydroxamie acid. Comparison of the effect of pH on the action of SHAM on cyanide-resistant respiration inR. glutinis, on the concentration of dissociated and undissociated form of SHAM in the intracelluler fluid and on its chelating ability refutes the notion that chelation of nonheme iron forms the basis of inhibiton of the alternative oxidase.
KeywordsHydroxamic Acid Alternative Oxidase Nonheme Iron Resistant Respiration Rhodotorula Glutinis
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