naphthoquinones and menadiol

It has been suggested that the enzymes DT-diaphorase and superoxide dismutase act in concert to prevent redox cycling of naphthoquinones and thus protect against the toxic effects of such substances. Little is known, however, about the scope of this process or the conditions necessary for its operation. In the presence of low levels of DT-diaphorase, 2-methyl-1,4-naphthoquinone was found to undergo redox cycling. This was very effectively inhibited by SOD, and in the presence of both enzymes the hydroquinone was maintained in the reduced form. The inhibitory effect of the enzyme combination was overcome, however, at high concentrations of the quinone, or by small increases in pH. Furthermore, redox cycling was re-established by addition of haemoproteins such as cytochrome c and methaemoglobin. DT-diaphorase and SOD strongly inhibited redox cycling by 2,3-dimethyl- and 2,3-dimethoxy-1,4-naphthoquinone, but not that of 2-hydroxy-, 5-hydroxy- or 2-amino-1,4-naphthoquinone. Inhibition of redox cycling by a combination of DT-diaphorase and SOD is therefore not applicable to all naphthoquinone derivatives, and when it does occur, it may be overwhelmed at high quinone concentrations, and it may not operate under slightly alkaline conditions or in the presence of tissue components capable of initiating hydroquinone autoxidation.

Topics: Animals; Cattle; Cytochrome c Group; Dicumarol; Electron Transport Complex IV; Hemoglobins; Hydrogen-Ion Concentration; Methemoglobin; NAD(P)H Dehydrogenase (Quinone); Naphthoquinones; Oxidation-Reduction; Oxygen; Rats; Superoxide Dismutase; Time Factors; Vitamin K

The quinol oxidase appears to be mainly responsible for the oxidation of the bacterial MKH2 in Bacillus subtilis W23 growing with either glucose or succinate. The activity of the enzyme was maximum with dimethylnaphthoquinol, a water-soluble analogue of the bacterial menaquinol. Menadiol or duroquinol were less actively respired, and naphthoquinol was not oxidized at all. After fourtyfold purification the isolated enzyme contained 5.3 mumol cytochrome aa3 per gram of protein and negligible amounts of cytochrome b and c. The turnover number based on cytochrome aa3 was about 10(3) electrons.s-1 at pH 7 and 37 degrees C. The preparation consisted mainly of a M(r) 57,000 and a M(r) 36,000 polypeptide. The N-terminal amino acid sequence of the latter polypeptide differed from that predicted by the qoxA gene of B. subtilis strain 168 (Santana et al. 1992), in that asp-14 predicted by qoxA was missing in the M(r) 36,000 polypeptide.

Topics: Amino Acid Sequence; Bacillus subtilis; Chromatography, Ion Exchange; Electron Transport Complex IV; Genes, Bacterial; Hydroquinones; Molecular Sequence Data; Naphthoquinones; Oxidation-Reduction; Vitamin K

Topics: Amides; Bromine; Chromatography; Dimethylformamide; Diphosphates; Naphthoquinones; Oxidation-Reduction; Phosphates; Phosphorus Isotopes; Phosphorylation; Research; Solvents; Ultraviolet Rays; Vitamin K

Topics: Bronchi; Bronchial Neoplasms; Carcinoma; Humans; Naphthoquinones; Vitamin K

Topics: Antifibrinolytic Agents; Hexosephosphates; Hexoses; In Vitro Techniques; Monoiodotyrosine; Naphthoquinones; Pentose Phosphate Pathway; Thyroid Gland; Tyrosine; Vitamin K

Topics: Antifibrinolytic Agents; Humans; Naphthoquinones; Neoplasms; Retinoids; Vitamin K

Topics: Antifibrinolytic Agents; Bilirubin; Humans; Infant, Newborn; Infant, Premature; Naphthoquinones; Vitamin K

Topics: 3-Hydroxyanthranilic Acid; Aminobenzoates; Animals; Erythrocytes; Mice; Naphthoquinones; Tryptophan; Vitamin K

Topics: Antifibrinolytic Agents; Humans; Infant, Newborn; Infant, Premature; Naphthoquinones; Vitamin K

Topics: Antifibrinolytic Agents; Hemostatics; Humans; Infant; Infant, Newborn; Naphthoquinones; Prothrombin; Vitamin K; Vitamin K 1

Topics: Antifibrinolytic Agents; Hemostatics; Humans; Infant, Newborn; Naphthoquinones; Prothrombin Time; Vitamin K; Vitamin K 1

Topics: Animals; Naphthoquinones; Rabbits; Rats; Vitamin K; X-Rays

Topics: Antifibrinolytic Agents; Naphthoquinones; Retinoids; Sodium; Vitamin K

Topics: Animals; Antifibrinolytic Agents; Chickens; Naphthoquinones; Vitamin K; Vitamin K 1; Vitamin K 3; Vitamin K Deficiency

Topics: Animals; Antifibrinolytic Agents; Naphthoquinones; Rats; Retinoids; Vitamin K; Water

Topics: Animals; Antifibrinolytic Agents; Naphthoquinones; Neoplasms, Experimental; Vitamin K; X-Rays