In order to study the safety of food additives with regard to their effects on alimentary tract, we examined the effects of food colors on leucine aminopeptidase activity and amino acid uptake in rat small intestine.
Leucine aminopeptidase activity in the homogenate of intestinal mucosa was estimated by use of leucine-β-naphthylamide as the substrate. Amino acid uptake was examined by the tissue accumulation method of α-aminoisobutyric-3-
14C-acid in intestinal segment of rat. The results obtained are as follow;
(1) The leucine aminopeptidase activity in mucosal homogenate was extremely decreased by the addition of xanthene or triphenylmethane colors to the incubation mixture (final concentration; 10
-4M), although azo and indigoid colors gave no effect.
(2) Decrease in the enzyme activity was not observed by sorbate, saccharin and other several food additives. Xanthene-related compounds, fluorescein and certain halogenated fluorescein derivatives, inhibited leucine aminopeptidase activity.
(3) Lineweaver-Burk's plot showed that inhibition of xanthene colors was “uncompetitive type”.
(4) Tissue accumulation of α-aminoisobutyric acid in intestine was inhibited by xanthene color, phloxine, in the same rate as the metabolic inhibitors, cyanide and 2, 4-dinitrophenol. However, other types of colors did not give the inhibitory effect.
(5) The declines of leucine aminopeptidase activity and amino acid uptake were not observed with the rats administrated food color
per os for three months.
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