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ß-Carotene 15,15'-Dioxygenase Activity is Responsive to Copper and Iron Concentrations in Rat Small Intestine

Phytonutrients Laboratory (A.D., J.C.S.), USDA-ARS, Beltsville Human Nutrition Research Center, Beltsville, Maryland
Nutrient Requirements and Functions Laboratory (M.F., C.G.L.), USDA-ARS, Beltsville Human Nutrition Research Center, Beltsville, Maryland

View larger version (39K): [in a new window]   Fig. 1. Effects of two levels of dietary iron (44 and 87 µg/g diet) in relation to the copper status on intestinal ß-carotene 15,15'-dioxygenase activity expressed as specific activity [pmol retinal/(h.mg protein)]. Weanling male rats fed one of the following diets for four weeks: diet 1—copper-adequate, normal iron (NFe); diet 2—copper-adequate, high iron (HFe); diet 3—copper-deficient, NFe; and diet 4—copper-deficient, HFe [with copper-adequate (6.0 µg Cu/g diet) and copper-deficient (0.6 µg Cu/g diet)]. Enzyme assays were conducted as described in MATERIALS AND METHODS. Values represent mean±SEM (n=4 rats each for diets 1 and 3, n=8 rats for diet 2, and n=9 rats for diet 4). Main effects and interactions of dietary copper and iron on the enzyme activity were examined by two-way ANOVA analysis; Cu effect, p<0.01; Fe effect, NS; CuxFe effect, NS with NS=non significant. Multiple comparisons of means among groups were assessed using Fisher’s test. Means with different letters were significantly different; (a,b) and (b,c): p<0.02 and (a,c): p<0.0001.

View larger version (24K): [in a new window]   Fig. 2. Linear relationships between ß-carotene 15,15'-dioxygenase activity [pmol retinal/(h.mg protein)] and either A) iron concentration or B) copper concentration in rat small intestine. Individual values are shown for the four dietary groups according to the following: () copper-adequate, normal iron (NFe); () copper-adequate, high iron (HFe); (bull;) copper-deficient, NFe; and () copper-deficient, HFe (see Fig. 1 for diet composition). The coefficients of correlation r1 (dioxygenase versus iron) and r2 (dioxygenase versus copper) were obtained by simple-regression analysis; test of significance of the linear relationships was determined by ANOVA.