Page 283 - Biochemistry PharmD General

4. Methemoglobin

In RBC the iron of hemoglobin is normally in ferrous
(Fe2+) form, but it is readily oxidized to the ferric (Fe3+)
form by hydrogen peroxide formed by RBC cell
metabolism, to yield met-hemoglobin. Ferric iron is
incapable of binding O2 therefore the functions of
hemoglobin are disturbed. Normally 1.7 to 2.4 % of total
hemoglobin will be in the form of met-hemoglobin.
Increase in the percent of met-hemoglobin is prevented
by the peroxidase action of a naturally occurring peptide
known as glutathione present in the RBC. Met-
hemoglobin is dark brown in colour.

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