Glutathione reductase activity and pyridoxine (pyridoxamine) phosphate oxidase activity in the red cell

The red-cell enzymes, glutathione reductase (FAD-dependent) and pyridoxine (pyridoxamine) phosphate oxidase (FMN-dependent), were studied in control subjects. The wide range in the glutathione reductase activity correlated inversely with the percentage stimulation by FAD added in vitro, and with pyridoxine (pyridoxamine) phosphate oxidase activity. Both enzymes were stimulated after ingestion of riboflavin. The results support the suggestion that the rate of metabolism of riboflavin in the red cell controls the activity of both enzymes, and the rate of red-cell metabolism of vitamin B-6.