The kinetics of the uptake of
Fe(II)-histidinate, a known promoter of lipid peroxidation, into
Ehrlich ascites tumor (EAT) cells and the intracellular binding of
iron were studied in vitro. EAT cells (27.10(6)/ml) were incubated in Hanks' balanced
salts solution at 37 degrees C for various time intervals in the presence of FeSO4 (1 mM) and
L-histidine (10 mM). Total
iron was determined by the 1,10-
phenanthroline/ascorbate method and ferric
iron by reaction with
5-sulfosalicylic acid; the difference was ascribed to ferrous
iron. Total
iron decreased rapidly in the medium (242 nmol within the first 10 min), and a corresponding increase of total
iron (saturation value 376 nmol after 60 min) was determined within the cells, after the cellular
proteins had been solubilized with 6 M
urea. In the absence of EAT cells,
Fe(II)-histidinate was readily oxidized to Fe(III)-histidinate by
oxygen, but this reaction was strongly retarded by the
tumor cells. The uptake of
iron histidinate occurred in the oxidized state, while an uptake of ferrous
iron could not be proven unambiguously. When EAT cells were saturated with
iron, it was found that 93% of intracellular
iron was bound to water-insoluble
proteins and 7% was associated with soluble
proteins, while no unbound
iron was detectable by the method used. It was concluded that, despite the high uptake of total
iron, only a very small portion of the intracellular
iron was available as a redox catalyst for lipid peroxidation.