[Express method for detecting benzidine dianisidine with sodium hypochlorite].

Oxidation of guaiacol by peroxidases in the presence of H2O2 is the basis for a widely used colorimetric assay. However, the nature of the assay product, which has an absorption maximum around 470 nm, had not been determined. In the present study, we combined HPLC with a rapid scanning uv-visible detector and observed a single product with a spectrum identical to the assay product from the reaction catalyzed by lactoperoxidase. Analysis of the reaction product using on-line HPLC with atmospheric pressure chemical ionization detection (LC-APCI/MS) yielded a mass spectrum consistent with 3,3 '-dimethoxy-4,4'-biphenylquinone. A minor reaction product was observed with mass spectrum consistent with 3,3'-dimethoxy-4,4'-dihydroxybiphenyl. The presence of a catechol impurity in guaiacol was previously shown to yield an additional product from peroxidase-mediated oxidation based on its visible absorption (Taurog et al., 1992 Anal. Biochem. 205, 271-277). When such an incubation mixture was analyzed using LC-APCI/MS, a product with mass spectrum consistent with 3-methoxy-2',3',4-trihydroxybiphenyl was observed. Identification of such a heterodimeric product supports the previously proposed mechanism for catechol interference in the guaiacol assay as well as the radical nature of peroxidase-catalyzed oxidation of phenols.

Biphenyl Compounds↗

PubMed1997

Three of the seven bphC genes of Rhodococcus erythropolis TA421, isolated from a termite ecosystem, are located on an indigenous plasmid associated with biphenyl degradation.

Rhodococcus erythropolis TA421, a polychlorinated biphenyl and biphenyl degrader isolated from a termite ecosystem, has seven bphC genes expressing 2,3-dihydroxybiphenyl dioxygenase activity. R. erythropolis TA421 harbored a large and probably linear plasmid on which three (bphC2, bphC3, and bphC4) of the seven bphC genes were located. A non-biphenyl-degrading mutant, designated strain TA422, was obtained spontaneously from R. erythropolis TA421. TA422 lacked the plasmid, suggesting that the three bphC genes were involved in the degradation of biphenyl. Southern blot analyses showed that R. erythropolis TA421 and Rhodococcus globerulus P6 have a similar set of bphC genes and that the genes for biphenyl catabolism are located on plasmids of different sizes. These results indicated that the genes encoding the biphenyl catabolic pathway in Rhodococcus strains are borne on plasmids.

Biphenyl Compounds↗

PubMed1996

Alterations of rings B and C of colchicine are cumulative in overall binding to tubulin but modify each kinetic step.

The role of the elimination of ring B and/or the modification of ring C of colchicine in tubulin binding kinetics and thermodynamics has been characterized, using four different molecules. These ligands are colchicine (COL); 2-methoxy-5-(2',3',4'-trimethoxyphenyl)-2,4,6-cycloheptatrien-1-on e (MTC), in which the central ring B has been reduced to one bond; allocolchicine (ALLO), in which ring C has been replaced by a six-membered ring; and 2,3,4-trimethoxy-4'-carbomethoxy-1,1'-biphenyl (TCB), where the same two modifications are made simultaneously. This paper describes the kinetics of association of ALLO with tubulin. The binding is accompanied by a fluorescence increase with slow biphasic kinetics, indicating binding to fast and slow tubulin isotypes. Binding to each of these isotypes occurs in two steps: a fast initial binding followed by a slower isomerization step. The K1 and k2 values for ALLO at 25 degrees C are 14,000 +/- 2,000 and 25,000 +/- 6,000 M-1 (fast and slow isotypes) and 0.055 +/- 0.003 s-1 and 0.013 +/- 0.001 s-1 (fast and slow isotype), respectively. For ALLO the reaction standard enthalpy change of the initial binding is 68 +/- 5 kJ.mol-1 (fast isotype) and 45 +/- 33 kJ.mol-1 (slow isotype) and the activation energy for the second forward step is 58 +/- 14 kJ.mol-1 (fast isotype) and 81 +/- 17 kJ.mol-1 (slow isotype). Displacement kinetics of bound ALLO by podophyllotoxin was monoexponential. The activation energy for the isomerization in the off direction is 107 +/- 7 kJ.mol-1. Comparison of the thermodynamic parameters for all four compounds shows that the modifications of both rings are cumulative with respect to overall binding. For the intermediate state there is a mutual influence of both modifications, suggesting an alteration of the reaction pathway.

Biphenyl Compounds↗