Intestinal iron absorption is recognized to be supported mainly by an active transport system, which requires energy consumption. Accordingly, it is reasonable to consider that Fe²⁺ or Fe³⁺ dependent ATPase activity may participate in intestinal iron absorption, as well as in the case of Ca²⁺ absorption, in which Ca²⁺ dependent ATPase plays an important role in the process. An attempt was made to identify the presence of Fe²⁺ or Fe³⁺ dependent ATPase in the rat intestinal mucosa.
Whole particulate suspension (WPS), from rat intestinal mucosa was used as the enzyme source. Eight mM ascorbic acid (Asc) or 1 mM citric acid (Cit) was added to the incubation mixture so as to prevent spontaneous oxidation of Fe²⁺ or hydroxylation of Fe³⁺ respectively. The increase of ATPase activities were apparently observed as the function of Fe²⁺ concentrations. The increase of Fe²⁺ dependent ATPase activities was higher in the presence of Asc than in no Asc condition.
Km values of Fe²⁺ ATPase activity were 0.4 mM or 5.3 mM ;in the case of Asc (+) or Asc (-) respectively, and there was statistical difference between these values (p<0.001). However, Fe³⁺ dependent ATPase activity was not observed in the presence of Cit in this system. The activities of Fe²⁺ dependent ATPase in the presence of Asc was approximately a half of Mg²⁺- or Ca²⁺-ATPase activities in WPS. But the dependency on metal ions was dominant for Fe²⁺ comparing to Ca²⁺ or Mg²⁺. Fe²⁺ dependent ATPase activity was not sensitive to Ouabain, theophylline and L-phenylalanine at the concentrations showing inhibitory effects. ³²P-phosphorylated protein was identified from WPS in the presence of [γ-³²P] ATP and Fe²⁺, and the molecular weight of the protein was estimated as 97, 000 by SDS polyacrylamide gel electrophoresis. These results suggested the presence of Fe²⁺ dependent ATPase in the intestinal mucosa.