ASCORBATE-MEDIATED TRANSMEMBRANE-REDUCING SYSTEM OF THE HUMAN ERYTHROCYTE

Actively metabolizing human erythrocytes catalyze the extracellular reduction of ferricyanide to ferrocyanide. Because neither of these anions can enter the cell, reducing equivalents generated in the course of glycolysis must in some manner be transferred across the cell membrane, thereby resulting in ferricyanide reduction. The transmembrane reduction apparently is effected by ascorbic acid. This compound in its oxidized form (dehydroascorbate) rapidly entered the cell. Here it obtained reducing equivalents which appear to come from NADH made available at the level of glyceraldehyde 3-phosphate dehydrogenase. Once reduced, it left the cell as ascorbic acid and accomplished the non-enzymatic reduction of ferricyanide.