**4.1. Erythrocytes**

Erythrocytes, which contain hemoglobin, are blood cells that perform the transfer of oxygen and carbon dioxide between tissues. G6PD is an important enzyme that performs vital functions within all cells of the body (Greene, 1993). The quantity of active G6PD decreases during the life of an erythrocyte and also the older erythrocytes become vulnerable to oxidative stress. G6PD, an enzyme in the oxidative pentose phosphate pathway, converts the nicotinamide adenine dinucleotide phosphate (NADP+) into its reduced form NADPH. It is necessary for the protection against oxidative stress in erythrocytes. The cells cannot eliminate this stress, which causes hemolysis of erythrocytes. Because H2O2 and other reactive oxygen species cannot be reduced, oxidation of hemoglobin to methemoglobin and membrane damage occur (Ruwende & Hill, 1998, Peters & Van Noorden, 2009).
