Iron-responsive
element-
binding protein (
IRE-BP) activity was studied in liver and intestinal samples of
hemochromatosis and control patients using a short 32P-IRE-RNA probe on "retardation" nondenaturing
polyacrylamide gels.
IRE-BP activity was assessed in liver biopsy specimens in 36 patients--16
hemochromatosis homozygotes, 4
hemochromatosis heterozygotes, 6 patients with secondary
iron overload, and 10 control patients with normal hepatic
iron concentrations. Intestinal
IRE-BP activity was assessed in 14
hemochromatosis homozygotes and 16 normal subjects. Endogenous
IRE-BP activity was determined from 32P retarded on the gel, and total
IRE-BP activity was assessed after reducing tissue samples with
2-mercaptoethanol. Hepatic endogenous
IRE-BP activity was inversely related to hepatic
iron concentration (r = .59, P < .0002). Mean hepatic endogenous
IRE-BP activity in the
hemochromatosis homozygotes, 0.25 +/- 0.04 pmol/mg
protein, was significantly decreased compared with values in the normal controls, 0.45 +/- 0.06 pmol/mg
protein, P < .05. Hepatic total
IRE-BP was also significantly decreased in the
hemochromatosis patients by gel retardation assay and Western blotting with anti-
IRE-BP antibody. Intestinal endogenous
IRE-BP activity, total
IRE-BP activity, and
iron concentration did not significantly differ between
hemochromatosis patients and normal control subjects. This suggests that both endogenous
IRE-BP activity and the total amount of the
protein are downregulated in the liver by tissue
iron. Intestinal
IRE-BP activity that regulates intestinal
transferrin receptor expression is normal in
hemochromatosis and appropriate for the intracellular
iron concentration.