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The mutagenicity of N,N-dimethytaminoazobenzene (DAB) is difficult to demonstrate in Ames' test. Usually there are specific requirements for activation by post-mitochondrial supernatant fluid (S-9) from Aroclor-treated rat livers and the pre-incubation modification of the test. Results from this laboratory suggest, however, that pre-incubation is not essential; also, that, contrary to published reports, concentrations of S-9 >10% in S-9 mix do not reduce the mutagenic response. Induction of enzyme activity well above normal levels, on the other hand, is necessary, but this requirement can be substituted by the addition of norharman. If a competent S-9 mix is used, pre-incubation with or without shaking does not alter the response and supplementation with ATP or NADH similarly has no effect. It is concluded that interiaboratoiy differences in the ability to demonstrate DAB mutagenicity reflect differences in the level of induction of liver enzymes and, possibly, the concentration of endogenous co-factors. [ABSTRACT FROM PUBLISHER]

The detection of certain bis-azo biphenyl dyes (Trypan blue, Evans blue and Congo red) by a modification of the standard Ames test protocol is reported. Detection of a mutagenic response required both the inclusion of FMN in S-9 mix and use of a pre-incubation step prior to addition of topagar and pouring in the usual manner. Evidence is presented to substantiate the proposal that use of this protocol provides optimal conditions for the two stages of activation required for the production of mutagenic metabolites from these dyes. These are (i) initial flavin-mediated (hepatic) azo reduction resulting in the formation of proximate mutagenic metabolites followed by (ii) the oxidative metabolism by S-9 resulting in the formation of ultimately mutagenic products. [ABSTRACT FROM PUBLISHER]