Histidine-stimulated divalent metal uptake in human erythrocytes and in the erythroleukaemic cell line HEL.92.1.7

The uptake of Zn-65 by human erythrocytes was investigated in the presence of high (40 mm) and low (5 mm) concentrations of histidine and 0-500 muM cobalt, nickel, manganese and zinc. Varying concentrations of metal mono- and bis-histidine complexes will be formed and the inhibition of Zn-65 uptake could be correlated with the calculated complex concentrations to investigate competition between metals. For each metal, the calculated concentrations of bis-histidine complex giving 50% inhibition of Zn-65 uptake were similar at both 5 mm and 40 mm histidine. Manganese-bis-histidine appeared to have a much higher affinity for the binding site than the other metal-bis-histidine complexes, which had similar affinities to each other. Studies of the inhibition of histidine-stimulated Mn-54 uptake by the addition of manganese confirmed that manganese-bis-histidine does act as a substrate for the transporter in a similar fashion to the other metals studied. In addition, human erythroleukaemic cells (HEL cells) were used as a model for erythroid precursor cells. L-histidine, but not D-histidine, stimulated Zn-65 uptake in a saturable fashion. The other metals competed with zinc in a similar manner to that seen in erythrocytes, and the affinity for manganese-bis-histidine was much greater than for the bis-histidine complexes of the other three metals. Both the capacity for metal transport per cell, and the affinity of the transporter for the metal-bis-histidine complexes, were much greater in the HEL cells than in the erythrocyte. It is suggested that histidine-stimulated metal transport may play a role in the supply of metals to maturing erythroid cells