Interference by the Carcinogenic 4-Nitro-quinoline N-Oxide of Triptophan and Indole Uptake in Escherichia coli

Abstract

THE potent water-soluble carcinogen 4-nitroquinoline N-oxide (NQO) is remarkably versatile and thus represents a good means of discerning pre-requisites for carcinogenesis. NQO condenses readily with sulphydryl groups; is mutagenic to bacteria, tobacco mosaic virus, and Aspergillus niger¹; inhibits incorporation of phosphorus-32 into nucleic acids of Ehrlich ascites carcinoma cells²; induces nucleolar ‘caps’ in Chang liver cells³; and inhibits growth of the flagellates Ochromonas danica, Euglena gracilis, of Corynebacterium bovis, and of the photosynthetic purple bacterium Rhodopseudomonas palustris. These growth inhibitions are competitively annulled by L-tryptophan; D-tryptophan is also effective. The competitive annulment ratio is 0.2 mg/ml. tryptophan: NQO 2 µ/ml.