NADPH OXIDASE SYSTEM AS A SUPEROXIDE-GENERATING CYANIDE-RESISTANT PATHWAY IN THE RESPIRATORY-CHAIN OF CORYNEBACTERIUM-GLUTAMICUM

The respiratory chain of Corynebacterium glutamicum was investigated, especially with respect to a cyanide-resistant respiratory chain bypas s oxidase. The membranes of C. glutamicum had NADH, succinate, lactate , and NADPH oxidase activities, and menaquinone, and cytochromes a(598 ), b(562(558)), and C-550 as respiratory components. The NADH, succina te, lactate, and NADPH oxidase systems, all of which were more cyanide -resistant than N, N, N', N'-tetramethyl-p-phenylene diamine oxidase a ctivity (cytochrome aa(3) terminal oxidase), had different sensitiviti es to cyanide; the cyanide sensitivity of these oxidase systems increa sed in the order, NADPH, lactate, NADH, and succinate. Taken together with the analysis of redox kinetics in the cytochromes and the effects of respiratory inhibitors, the results suggested that there is a cyan ide-resistant bypass oxidase branching at the menaquinone site, beside s cyanide-sensitive cytochrome oxidase in the respiratory chain. H+/O measurements with resting cells suggested that the cyanide-sensitive r espiratory chain has two or three coupling sites, of which one is in N ADH dehydrogenase and the others between menaquinone and cytochrome ox idase, but the cyanide-resistant bypass oxidase may not have any proto n coupling site. NADPH and lactate oxidase systems were more resistant to UV irradiation than other systems and the UV insensitivity was hig hest in the NADPH oxidase system, suggesting that a specific quinone r esistant to UV or no such a quinone works in at least NADPH oxidase sy stem while the UV-sensitive menaquinone pool does in other oxidase sys tems. Furthermore, superoxide was generated in well-washed membranes, most strongly in the NADPH oxidase system. Thus, it was suggested that the cyanide-resistant bypass oxidase system of C. glutamicum is relat ed to the NADPH oxidase system, which may be involved in generation of superoxide anions and probably functions together with superoxide dis mutase and catalase.