Effects on quercetin mutagenicity

Exposure of quercetin to buffers in an oxygen atmosphere had no observable effect on quercetin mutagenicity in the pH range 2 to 5. The transition point for the pH-oxygen inactivation appears to be near pH 6.5, since the number of revertants at this pH was about 440 compared to about 1000 at the lower pH values. Complete inactivation, where the number of revertants equals that observed with buffer controls, took place at pH values above 8. 

Limited studies showed that the following enzymes had no or only minor effects on quercetin mutagenicity under conditions similar to those used for tyrosinase (1 100 weight ratio enzyme to quercetin 50% pH 7.5 buffer ethanol 37 C 2 hours) catalase, lipoxygenase, peroxidase, and superoxide dismutase. Additional studies are needed to define the ability of these oxidizing enzymes to modify flavonoids over a broader pH range. 

Table 4. Effect of temperature on quercetin mutagenicity (exposure for 3 hours at pH 7.5 and 9.0 in the presence of oxygen).

These results strikingly demonstrate the minor influence of temperature compared to the major effect of pH on quercetin mutagenicity. 

Table 8. Effect of metal salts on quercetin mutagenicity. ...

Ogawa, S., Hirayama, T., Nohara, M., Tokuda, M., Hirai, K., and Fukui, S., The effect of quercetin on the mutagenicity of 2-acety laminofluorene and benzo[alpha]pyrene in Salmonella typhimurium sitams,. Mutation Res., 142, 103-107, 1985. 

FACTORS WITH FACILITAE QUERCETIN MUTAGENICITY Table 6. Effect of time on the mutagenicity of quercetin at pH 7.5 and 537 9.O. . 

The structural requirements for 8-hydroxyflavone activation are distinct from those for flavonols such as quercetin or kaempferol. Whereas B-ring hydroxylation, 2,3-unsaturation, and 3-hy-droxylation appear critical for flavonol mutagenicity, the B-ring and 2,3-positions do not appear to be involved in the activation of 8-substituted flavones. The 5,7,8-substitution pattern on the A-ring is particularly effective at conferring high activity in the flavone series. The seven most active compounds known at present all have -OH or -OCH substituents at these positions. 

Table 2. Effect of pH on the activity of Salmonella typhimurium in the presence of quercetin (15 mg in 100 ml 50% ethanol-buffer). All pH values are adjusted to 7.5 for the mutagenicity assays.

Table 9. Effect of cobaltous chloride and manganous chloride on mutagenic activity of quercetin.

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