49] Methemoglobin reduction system of erythrocytes

Abstract

Publisher Summary This chapter describes the methemoglobin reduction system of erythrocytes. The methemoglobin reduction system is the enzyme system of red blood cells catalyzes the reduction of the four ferric ions of methemoglobin to ferrous ions. This reduction proceeds at a rate that is sufficient to maintain approximately 99% of the hemoglobin in its ferrous state, despite the continuous conversion of hemoglobin to methemoglobin by various oxidants of the cell. Under normal conditions, most of the methemoglobin reduction can be attributed to catalysis by an NADH- utilizing system. NADPH-utilizing enzymes, which have also been isolated from erythrocytes, appear to have little role in methemoglobin reduction under normal conditions. The involvement of a second component in the methemoglobin reduction system was suggested by the observation that the rate of methemoglobin reduction catalyzed by purified reductase was slow relative to the rate that occurs in intact cells. Similar NADH-reductases have been reported to be present in erythrocytes of many species. A highly purified NADH-dependent cytochrome b 5 reductase has been isolated from bovine erythrocytes.