Purification and characterization of the Mycobacterium smegmatis catalase-peroxidase involved in isoniazid activation.

The unique antitubercular activity of isoniazid requires that the drug be oxidized by the katG-encoded mycobacterial catalase-peroxidase to an activated drug form. In order to quantitatively assess the catalytic capabilities of the enzyme, the native catalase-peroxidase from Mycobacterium smegmatis was purified over 200-fold to homogeneity. The enzyme was shown to exhibit both catalase and peroxidase activities, and in the presence of either hydrogen peroxide or t-butyl peroxide, was found to catalyze the oxidation of the reduced pyridine nucleotides, NADH and NADPH, as well as artificial peroxidase substrates, at rates between 2.7 and 20 s-1. The homogeneous enzyme exhibited a visible absorbance spectrum typical of ferric heme-containing catalase-peroxidases, with a Soret maximum at 406 nm. Low temperature (10 K) electron paramagnetic resonance spectra in the presence of ethylene glycol revealed a high spin Fe(III) signal with g values of 5.9 and 5.6. The enzyme was very slowly (t1/2 = approximately 20 min) reduced by dithionite, and the reduced form showed typical spectral changes when either KCN or CO were subsequently added. The M. smegmatis catalase-peroxidase was found to contain 2 heme molecules per tetramer, which were identified as iron protoporphyrin IX by the pyridine hemochromogen assay. The peroxidatic activity was inhibited by KCN, NaN3, isoniazid (isonicotinic acid hydrazide), and its isomer, nicotinic acid hydrazide, but not by 3-amino-1,2,4-triazole. The role of mycobacterial catalase-peroxidases in the oxidative activation of the antitubercular prodrug isoniazid is discussed.

Antioxidant effects of angiotensin-converting enzyme (ACE) inhibitors: free radical and oxidant scavenging are sulfhydryl dependent, but lipid peroxidation is inhibited by both sulfhydryl- and nonsulfhydryl-containing ACE inhibitors.

With an assay that generates free radicals (FR) through photooxidation of dianisidine sensitized by riboflavin, 4 x 10(-5) M captopril, epicaptopril (SQ 14,534, captopril's stereoisomer), zofenopril, and fentiapril [all sulfhydryl (-SH)-containing angiotensin-converting enzyme (ACE) inhibitors] were shown effective scavengers of nonsuperoxide free radicals whereas non-SH ACE inhibitors were not. Captopril was a more effective FR scavenger at pH 5.0 than at pH 7.5. Captopril (2 x 10(-5) M) also scavenged the other toxic oxygen species hydrogen peroxide and singlet oxygen and inhibited microsomal lipid peroxidation. Finally, captopril reduced the amount of superoxide anion-radical detected after neutrophils in whole blood were activated with zymosan, probably by inhibiting leukocyte superoxide production.

Mutagenicity of benzidine and benzidine-congener dyes and selected monoazo dyes in a modified Salmonella assay.

We have evaluated the mutagenic activity of a series of diazo compounds derived from benzidine and its congeners o-tolidine, o-dianisidine and 3,3'-dichlorobenzidine as well as several monoazo compounds. The test system used was a modification of the standard Ames Salmonella assay in which FMN, hamster liver S9 and a preincubation step are used to facilitate azo reduction and detection of the resulting mutagenic aromatic amines. All of the benzidine and o-tolidine dyes tested were clearly mutagenic. The o-dianisidine dyes except for Direct Blue 218 were also mutagenic. Direct Blue 218 is a copper complex of the mutagenic o-dianisidine dye Direct Blue 15. Pigment Yellow 12, which is derived from 3,3'-dichlorobenzidine, could not be detected as mutagenic, presumably because of its lack of solubility in the test reaction mixture. Of the monoazo dyes tested, methyl orange was clearly mutagenic, while C.I. Acid Red 26 and Acid Dye (C.I. 16155; often referred to as Ponceau 3R) had marginal to weak mutagenic activity. Several commercial dye samples had greater mutagenic activity with the modified test protocol than did equimolar quantities of their mutagenic aromatic amine reduction products. Investigation of this phenomenon for Direct Black 38 and trypan blue showed that it was due to the presence of mutagenic impurities in these samples. The modified method used appears to be suitable for testing the mutagenicity of azo dyes, and it may also be useful for monitoring the presence of mutagenic or potentially carcinogenic impurities in otherwise nonmutagenic azo dyes.

Chemical linkage of erythrocytes and viral antigen in the hemolysis-in-gel (HIG) test for viral antibodies.

The sensitivity of the hemolysis-in-gel (HIG) test with rubella antigen is not improved by chemical linkage of the virus to the erythrocytes, and after such modification, IgM specific antibodies are not detectable. In the influenza HIG test with tetraazotized o-dianisidine (TOD), chromic chloride and potassium periodate as coupling reagents, increased sensitivity was observed with allantoic fluid of infected eggs as antigen. If Tween-ether treated hemagglutinin is used in the HIG test, zones of hemolysis are detectable only after treatment of the erythrocytes with TOD, chromic chloride and potassium periodate.

[Cooxidation of potassium ferrocyanide and o-dianisidine by hydrogen peroxide catalyzed by horseradish peroxidase. Substrate-substrate activation]. / Sovmestnoe okislenie ferrotsianina kaliia i o-dianizidina perekis'iu vodoroda, kataliziruemoe peroksidazoi iz khrena. Substrat-substratnaia aktivatsiia.

The kinetics of cooxidation of potassium ferrocyanide and o-dianisidine by hydrogen peroxide catalyzed by horseradish peroxidase were studied. The peroxidation of potassium ferrocyanide is activated by o-dianisidine. A scheme illustrating the direct involvement of the enzyme in substrate-substrate activation is proposed. A method for determination of the rate constants of the first electron transfer from o-dianisidine to peroxidase (i. e. reduction of peroxidase E1 to E2) and of the constants for o-dianisidine binding by E1 was developed.

Inhibition of bovine adrenocortical cytochrome P-450scc by 3,3'-dimethoxybenzidine.

The effect of 3,3'=dimethoxybenzidine (o-dianisidine) on the conversion of cholesterol to pregnenolone was investigated in a reconstituted side chain cleavage system using enzymes purified from bovine adrenal cortex; d-p-aminoglutethimide was also assayed under similar conditions for comparison. 3,3'-Dimethoxybenzidine was found to be a potent inhibitor of pregnenolone formation, causing 50% inhibition at a concentration of 1.5 microM when using 70 microM cholesterol - this dose is approximately one fourth that required of 3-methoxybenzidine and one twentieth that required of benzidine for equal inhibition. In the same system, d-p-aminoglutethimide exhibited an I50 value of about 55 microM. No effects of 3,3'-dimethoxybenzidine on adrenodoxin reductase or adrenodoxin activities could be detected, and inhibition of side chain cleavage could be relieved by dilution suggesting that the inhibitor acts by reversibly binding to cytochrome P-450scc.

Testing of some benzidine analogues for microsomal activation to bacterial mutagens.

Analogues of benzidine were assayed for mutagenic activity towards Salmonella typhimurium TA 1538 in the presence and absence of a liver enzyme preparation. Purified 3,3'-dichlorobenzidine and the technical grade material had some direct mutagenic activity, but this was increased over 50-fold by addition of a liver mixed function oxidase preparation. In the presence of the liver preparation, 3,3'-dichlorobenzidine was approximately 10 times more active than benzidine, while 3,3',5,5'-tetrafluorobenzidine was of approximately equipotency. On the other hand, 3,3',5,5'-tetramethylbenzidine had no mutagenic activity alone or in conjunction with a liver preparation. 3,3'-Dianisidine had slight mutagenic activity in the presence of liver but none in its absence.

The formation of hydrogen peroxide during the oxidation of reduced nicotinamide adenine dinucleotide by cytochrome o from Vitreoscilla.

The formation of hydrogen peroxide during the oxidation of NADH by purified preparations of cytochrome o has been demonstrated by employing three independent methods: polarographic, colorimetric, and fluorometric. The first two methods were used to assay for the accumulation of hydrogen peroxide and showed that hydrogen peroxide did accumulate as a product, but only about 30% of the oxygen consumed or 15 to 20% of the NADH oxidized was recoverable as hydrogen peroxide. This lack of 1:1 stoichiometry was not due to residual catalase activity in these preparations which could be eliminated by freeze-thawing. Thus, hydrogen peroxide may not be the sole or primary product of the NADH-cytochrome o oxidase reaction. The fluorometric assay could be coupled directly to the NADH-cytochrome o oxidase reaction in one medium, and this method showed that hydrogen peroxide was generated continuously from the beginning of the reaction in a 1:1 stoichiometry, hydrogen peroxide generated to NADH oxidized. This result suggests that hydrogen peroxide is an intermediate that can be trapped efficiently under the conditions of the fluorometric assay, whereas under the conditions of the first two assays most of the hydrogen peroxide generated undergoes further reaction. Exogenously added FAD or FMN increased the percentage of hydrogen peroxide that accumulated in the NADHcytochrome o oxidase reaction. Flavin is believed to act on the reductase side of cytochrome o so the increased percentage of hydrogen peroxide is not likely to result from the direct reaction of reduced flavin with oxygen.