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J Bacteriol. 1972 May; 110(2): 628-632
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

Mode of Action of Oxathiin Systemic Fungicides V. Effect on Electron Transport System of Ustilago maydis and Saccharomyces cerevisiae

^a Department of Botany and Microbiology, Montana State University, Bozeman, Montana 59715

ABSTRACT

The systemic fungicide carboxin (5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide) at 100 µM inhibited succinate cytochrome c reductase in mitochondria from Ustilago maydis and Saccharomyces cerevisiae. It did not have any effect on reduced nicotinamide adenine dinucleotide (NADH) cytochrome c reductase. Succinate coenzyme Q reductase was also inhibited, but NADH coenzyme Q reductase was not. When dichlorophenolindophenol (DCIP) was used as the terminal acceptor of electrons from the oxidation of succinate, carboxin was very effective in inhibiting succinate-DCIP reductase. Carboxin was inhibitory to succinic dehydrogenase assayed with phenazine methosulfate plus DCIP when intact mitochondria were used as the enzyme source but not when solubilized enzyme was used. The main site of action of carboxin, therefore, appears to lie between succinate and coenzyme Q. The dioxide analogue of carboxin was also effective in inhibiting succinate-cytochrome c reductase, succinate-coenzyme Q reductase, or succinate-DCIP reductase, whereas the monoxide analogue was less effective in inhibiting these enzymes.

¹ Present address: Department of Microbiology and Biochemistry, Idaho State University, Pocatello, Idaho 83201.