Purification and Properties of a Plant Desmutagenic Factor for the Mutagenic Principle of Tryptophan Pyrolysate

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Abstract
A desmutagenic factor for Trp-P-2 which is a potent mutagen discovered by Sugimura and his colleagues in pyrolysis products of tryptophan has been identified from extracts of cabbage (Brassica oleracea) leaves. Analysis of this factor to determine its composition revealed that it had a molecular weight of 43,000 and contained 45.2 µg of sugar per mg of protein. The purified factor exhibited a hemo-protein-like absorption spectrum with a Soret band of 404 nm and α and β bands at 640 and 497 nm, respectively. In addition to counteracting the mutagenicity of Trp-P-2, the mutagenic activity of Trp-P-1, which is 4-methyl derivative of Trp-P-2, was equally abolished by the factor. Other mutagens, such as ethidium bromide and 2-amino-anthracene, were found to be susceptible to the factor, but it had no effect on such mutagens as ICR-170 and AF-2. Furthermore, the factor greatly enhanced the mutagenicity of 1,2-diamino-4-nitrobenzene. Several lines of investigations were pursued to determine the possible mode of action to explain the results obtained with the factor. These studies indicated that the factor was a peroxidase which possessed NADPH-oxidase activity. In this paper, the mechanism of the desmutagenic action of the factor is discussed with special reference to these enzymatic activities.