Absorption of heme iron.

Heme iron is absorbed from meat more efficiently than dietary inorganic iron and in a different manner. Thus, iron deficiency is less frequent in countries where meat constitutes a significant part of the diet. Proteolytic digestion of myoglobin and hemoglobin results in the release of heme, which is maintained in a soluble form by globin degradation products so that it remains available for absorption. Chelators that either diminish or enhance the absorption of inorganic iron have little effect on the absorption of heme iron. Heme enters the small intestinal absorptive cell as an intact metalloporphyrin. This may be facilitated by a vesicular transport system. In the absorptive cell the porphyrin ring is split by heme oxygenase. The released inorganic iron becomes associated with mobilferrin and paraferritin, which acts as a ferrireductase to make iron available for production of iron-containing end products such as heme proteins. Mucosal transfer of iron into the body occurs competitively with dietary iron that entered the absorptive cell as inorganic iron because they both share a common pathway within the intestinal cell.