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.