Properties of 3‐(3,4‐Dichlorophenyl)‐1,1‐dimethylurea and Other Inhibitors of the Cytochrome<i>bc</i>₁Segment of the Mitochondrial Respiratory Chain in<i>Saccharomyces cerevisiae</i>

Abstract

The properties of 3‐(3,4‐dichlorophenyl)1,1‐dimethylurea (diuron) are compared to those of antimycin, n ‐heptyl‐hydroxyquinoline‐ N ‐oxide (HpHOQnO), mucidin and funiculosin in submitochondrial particles of Saccharomyces cerevisiae . Diuron inhibits the transport of electrons between cytochromes b and c 1 of the respiratory chain of S. cerevisiae as do the other inhibitors. Kinetics of inhibition of NADH oxidase are non‐sigmoidal for the inhibitors of low affinities: diuron and HpHOQnO. Mucidin and funiculosin exhibit high apparent affinities similar to that of antimycin. However the sigmoidicity of the kinetics of inhibition is not apparent for these two inhibitors. Diuron and funiculosin do not induce the ‘red‐shift’ of cytochrome b 562 . In contrast to beef heart, HpHOQnO does induce the ‘red‐shift’ of cytochrome b 562 in S. cerevisiae . Diuron induces the ‘extra‐reduction’ of cytochrome b . Mucidin induces a ‘red‐shift’ but yields a very limited ‘extra‐reduction’ of cytochrome b . Our results demonstrate that the inhibition of respiration of the bc 1 segment of the respiratory chain are not necessarily related to the ‘red‐shift’ and the ‘extra‐reduction’ of the cytochrome(s) b . They raise the possibility of the existence in yeast mitochondria of two distinct inhibitor‐binding sites, each of which would be able to control the transfer of electrons between cytochromes b and c 1 ; in addition, one site would be responsible for the ‘red‐shift’ and the other would control the ‘extra‐reduction’ of cytochrome(s) b .