Effects of food dyes on Paramecium caudatum: toxicity and inhibitory effects on leucine aminopeptidase and acid phosphatase activity.

The toxic effect of 14 food dyes was studied in Paramecium caudatum. It was found that xanthene dyes containing halogen atoms in their molecules were more toxic than other groups of food dyes. Phloxin and rose bengal containing chlorine were especially toxic. The effect of food dyes on leucine aminopeptidase, acid phosphatase, and γ-glutamyl transpeptidase activity in P. caudatum was studied in order to investigate the mechanism of toxicity. Phloxin and rose bengal inhibited leucine aminopeptidase remarkably. The inhibitory effect of food dyes on leucine aminopeptidase in vitro is consistent with the toxic effect of the dyes on the survival time of P. caudatum. A possible correlation between toxicity and inhibition of the activity of enzymes involved in the digestive process is discussed.