Studies on the partition of iron in bone marrow cells.

Canine marrow cells were incubated with transferrin-bound (59)Fe, and the partition of cellular iron was studied by chromatographic and gel filtration methods. Splitting-off of iron from the stromal fraction was avoided by lysing the cells in Tris HCl buffer at pH 8.6. Cellular iron was divided into four major compartments: stroma, microsomes, main hemoglobin, and fraction I. The iron in fraction I was found in ferritin, heme proteins, and low molecular weight iron. With incubation times of 3-10 min, (59)Fe appeared promptly in the main hemoglobin. The entry of (59)Fe into ferritin paralleled that of hemoglobin but was smaller in amount. When the marrow cells were incubated with (59)Fe for 15-20 min and reincubated without radioactive iron, movement of (59)Fe into main hemoglobin was observed, and essentially all this iron came from the particulate fraction (stroma, mitochondria, and microsomes). In these chase experiments there was no change in the total quantity of (59)Fe in ferritin. There was no evidence of a significant hemoglobin precursor other than low molecular weight iron. DEPENDING UPON CONCENTRATION, LEAD WAS OBSERVED TO INHIBIT CELLULAR IRON METABOLISM AT SEVERAL POINTS: uptake of iron by the cell, movement of iron from stroma to the soluble intracellular compartment, and synthesis of hemoglobin. The most pronounced inhibitory effect of lead was always on hemoglobin synthesis with an increase in ferritin: hemoglobin ratio. Bipyridine appeared to trap intracellular ferrous iron and to inhibit synthesis of both hemoglobin and ferritin. It was concluded that iron moves from the stroma into the soluble intracellular compartment as low molecular weight iron, probably as a complex of ferrous iron with low molecular weight components of the cytoplasm, that serves as the source of iron for both hemoglobin and ferritin synthesis.