Enhancement of Iron Absorption From Ligated Segments of Rat Intestine by Histidine, Cysteine, and Lysine: Effects of Removing Ionizing Groups and of Stereoisomerism

The effectiveness of L-histidine, L-cysteine, and L-lysine in enhancing iron uptake from ligated, in vivo segments of duodenum was compared with that of several structurally similar compounds from which certain ionizing groups had been removed. Decarboxylation of histidine, removal of the ε-amino of lysine, and the substitution of either a hydrogen or hydroxyl group for the sulfhydryl of cysteine all resulted in a loss of their ability to enhance iron uptake. Thus it appears that the ability of these three amino acids to form tridentate chelates is essential to their effectiveness in enhancing iron uptake. Additionally, it was found that the L isomers were not significantly better than the D forms in enhancing iron uptake, suggesting that “active transport” of the L forms is of little quantitative significance in the enhancement of iron uptake.