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The suitability of Ehrlich ascites tumour cells as a test object for potential drugs affecting ATP-producing or consuming processes directly or indirectly is made likely by actions of local anesthetics and narcotics on the energy metabolism of these cells. The influence of local anesthetics on cation transport and Ca+(+)-dependent processes as well as the inhibition of NADH-ubiquinone reductase by narcotics is demonstrated for Ehrlich ascites tumour cells, too.

The actions of Dexon on the NADH-ferricyanide oxidoreductase and the NADPH oxidase system of electron transfer particles (ETP) from beef heart as well as on the NADPH-cytochrome c oxidoreductase from brewer's yeast (Saccharomyces carlsbergensis Hansen) were investigated. The inhibition of the NADH dehydrogenase activity of ETP and that of the yeast enzyme correspond with respect to the following characteristics: 1) increase in the inhibition, 2) enhancement of the Dexon sensitivity by one order of magnitude after preincubation in the presence of NAD(P)H, 3) irreversibility of the inhibition, 4) no detectable changes in the spectral properties and in coenzyme activity of FMN after acid extraction from Dexon-treated enzyme. The inhibition of the NADH dehydrogenase activity of ETP is diminished by both NAD+ and FMN. However, no interaction of Dexon with NAD(P)H or FMN could be detected in the absence of enzyme or apoenzyme. The concentration of half-inhibition by Dexon for the yeast enzyme corresponds with its FMN concentration. It is proposed that both apoenzyme, NAD(P)H and FMN are involved in the interaction with Dexon. Possible mechanisms of binding are both complanar complexations of the ring systems and a triazene formation between FMNH2 and Dexon. The NADPH oxidase activity of the ETP is partly inhibited; the share inhibited by Dexon may represent the pathway via the transhydrogenase reaction.

The fungicide dexon (p-dimethylaminobenzenediazosulfonate, Na-salt) inhibits the NADH oxidase activity of submitochondrial particles (ETP) from beef heart (semi-inhibition concentration 1.4 muM), while the succinate oxidase activity is unaffected. Measurements of the activity of several enzymatic partial reactions of the respiratory chain of ETP suggest that dexon acts directly on the flavine of NADH dehydrogenase. Soluble NADH-cytochrome c-oxidoreductase (MAHLER) and rotenone-insensitive NADH ubiquinone reductase are also inhibited by dexon. At low concentrations of dexon, inhibition of ETP starts slowly only after addition of NADH. Preincubation without NADH increases the amount of inhibition, but does not prevent the time delay. It is assumed that an electron flux through the respiratory chain, or reduction of flavine is prerequisite for the reaction of dexon with the action site. Furthermore, dexon inhibits the NADH dehydrogenase located at the outer surface of the inner membrane of plant mitochondria, accessible to extramitochondrial NADH and insensitive to rotenone, as has been shown on isolated mitochondria from cauliflower (Brassica oleracea L). In addition, dexon inhibits selectively the NADH dehydrogenase of the DT diaphorase (ERNSTER) from rat liver cytosol. In contrast, the dicoumarol-insensitive NADH dehydrogenase (ZINSMEYER et al.) from rat liver cytosol, the NADH-cytochrome b5-reductase (STRITTMATTER) from rat liver microsomes, the rotenone-insensitive NADH-cytochrome c-oxidoreductase of the outer membrane of rat liver mitochondria, soluble NADH-oxidase from Escherichia coli, and NADH-dehydrogenase from human erythrocytes are not inhibited. The results suggest that dexon is a group reagent to certain pyridine nucleotide-dependent flavine enzymes.