Abstract
The concentration of methemoglobin increases as red cells age in normals and in patients with congenital methemoglobinemia (CMHb), yet the activity of NADH diaphorase (ND) (Scott assay) does not decrease with age. A specific assay for methemoglobin reductase (MHR) (J. Lab. Clin. Med. 72.339, 1968) permits reassessment of this phenomenon. Red cells were separated by centrifugation at 100,000 g for 1 hour. The top and bottom 10% were harvested and mean ages determined by glutamic oxaloacetic transaminase (GOT) activity. The age stability of ND activity was confirmed. The MHR activity of old cells (bottom layer) was 15% lower than that of younger (top layer) cells in normal individuals. In one family with CMHb and two fast migrating isoenzyme variant of ND, the activity was only slightly reduced (12%) whereas MHR activity was markedly reduced (40 to 90%) in the old cells compared to young cells. An unrelated female with CMHb and a slow migrating variant of ND was previously reported to have “pseudo-mosaicism” on the basis of heterogeneous distribution of methemoglobin between her younger and older cells (NEJM 275:397, 1966). Her older cells actually had greater activity of ND than did her younger cells. In contrast, the MHR activity of her older cells was only 10% of her younger cells. Thus, the normal age-lability of MHR can account for the accumulation of methemoglobin as erythrocytes mature. Exaggeration of this tendency due to structural modifications in the enzyme molecules may account for methemoglobinemia in patients carrying variant isoenzymes.
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Feig, S., Nathan, D. & Zarkowsky, H. Age lability of normal and variant methemoglobin reductase. Pediatr Res 5, 409–410 (1971). https://doi.org/10.1203/00006450-197108000-00161
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DOI: https://doi.org/10.1203/00006450-197108000-00161