Figure 4.

Schematic representation of ascorbate (ASC) recycling between erythrocytes and plasma. Under normal conditions, the plasma membrane redox system (PMRS) and ascorbate free radical (AFR) reductase function to transfer reducing equivalents from intracellular electron donors to plasma. These electrons are used to reduce the AFR to reduced ASC. During aging, the condition of oxidative stress is generated in the plasma, leading to higher rate of conversion of ASC to AFR. The increase in erythrocyte AFR reductase/PMRS activity is a compensatory mechanism to protect against increased oxidative stress (Rizvi et al. 2009).