Synthesis of Riboflavin Nucleotides by Mature Human Erythrocytes

Intact human red blood cells can synthesize FAD and FMN from riboflavin.The rate of synthesis of FAD is linearlyproportional to the concentration of riboflavin in the medium at levels below 0.9µM. With 0.9 µM riboflavin, the rate ofsynthesis is about 0.1 mµmole FAD/ml.red blood cells/hour. Incubation of redblood cells with riboflavin can result inincreased red cell glutathione reductaseactivity when the enzyme is measured inthe absence of added FAD. This indicates that the FAD concentration in thered cells increased during the incubation. The rate of incorporation of radioactive riboflavin into red blood cells isthe same whether the cells are suspendedin plasma or in a phosphate-saline-glucose medium. The time it takes for halfthe FAD in normal human red bloodcells to turn over is calculated to beabout 6 days, assuming a single mixingpool of red cell FAD.

Submitted on March 9, 1970 Revised on April 28, 1970 Accepted on May 8, 1970