Variable mutagenic activity of commercial preparations of ABTS (2,2'-azino-di(3-ethyl-benz-thiazoline) sulphonic acid.

Different batches of ABTS obtained from the same commercial source varied in their capacity to effect direct mutation in the strains of Salmonella typhimurium used routinely in the incorporation test of Ames. One batch, obtained in 1976, and another obtained early in 1979, both exhibited direct base-pair substitution and frame-shift activities. These activities, however, were absent from each of two batches obtained after 1979, and also from a highly purified preparation from a different source. The possible presence of the unsulphonated immediate precursor of ABTS as a mutagenic impurity is an unlikely explanation for the activity of the mutagenic preparations. It is more probable that the commercial synthesis generated other, mutagenic, impurities which remained in the batches obtained in 1976 and early in 1979, but were absent or were removed from later batches. The identity of these active impurities is unknown. Pure ABTS is neither a direct nor an indirect mutagen.