Studies on the partition of iron in bone marrow cells

Abstract

A B S T R A C T Canine marrow cells were incubated with transferrin-bound 59Fe, 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, 59Fe appeared promptly in the main hemoglobin. The entry of 59Fe into ferritin paralleled that of hemoglobin but was smaller in amount. When the marrow cells were incubated with 59Fe for 15-20 min and reincubated without radioactive iron, movement of 59Fe 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 59Fe 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.

Erythrocyte Ferritin

“…If erythrocyte ferritin is mostly saturated with iron and is present normally in small amounts, this would fit best with the available evidence that ferritin iron is not available for hemoglobin synthesis [11,14]. However, this evidence was obtained using relatively short term experiments.…”

“…Chromatography with Sephadex G-200 was performed by the method of Primosigh and Thomas [11] with 0.005 M Tris-HCl buffer at pH 7.7 with 0.01 M EDTA.…”

“…The crystals were redissolved, recrystallized three times, and finally dissolved in a minimal amount of 0.05 M Tris-HCl, pH 7.7, with 0.01 M EDTA and chromatographed on Sephadex G-200 [11]. The ferritin fraction was collected, dialyzed against 0.25% sodium chloride with 0.02% sodium azide, and concentrated to approximately 15 mg/ml.…”

Brain Iron Homeostasis: From Molecular Mechanisms To Clinical Significance and Therapeutic Opportunities

“…Several different, though not mutually exclusive, hypotheses of iron transport to the mitochondrion have been proposed. The prevailing hypothesis suggests that the labile iron pool in the cytosol contributes to the mitochondrial iron content (357,368). Other studies suggest that Fe 2 + , once transported out of the endosome, is bound by hydrophobic pockets of chaperone proteins for transport to the mitochondria (369).…”

Detection and Quantitation of59Fe-Labeled Proteins Using Storage Phosphorimaging

“…Iron is bound to proteins by relatively weak bonds and nondissociative methods are needed to preserve iron compounds intact during their separation. Gel permeation chromatography was used to separate cellular iron-containing proteins after labeling the cells with radioactive iron (4,5,6,9). This technique suffers from low resolution and sensitivity, long separation times, and the difficulty in processing large numbers of samples in parallel.…”