"Glucose-6-phosphate dehydrogenase (G6PD, EC220.127.116.11) is expressed in all tissues where it is the first and rate-limiting enzyme of the pentose phosphate pathway (PPP) that consists of the oxidative and non-oxidative branches and usually works at 1â2% of its maximal potential in healthy subjects due to the high level of nicotinamide adenine dinucleotide phosphate (NADPH). The G6PD gene is wildly expressed, especially higher in red cells because PPP is the only pathway for generating reducing capacity in the erythrocyte. Active G6PD in human cells is a dimer or tetramer in a pH-dependent equilibrium, and each monomer is composed of 515 amino acids. The G6PD activity is regulated by the levels of NADP+ for sufficient supply of NADPH through stimulating as a substrate the activity of the enzyme directly and stabilizing the enzyme in the proper conformation. G6PD deficiency (lower activity due to the numerous point mutations) is classified into four classes by the WHO according to the
remaining activity of wild-type G6PD activity. These are described as: class I is <1%; class II is <10%; and class III is 10~60% of normal G6PD function. Class IV is 60~100% that is considered as normal G6PD activity. G6PD deficiency is the most common enzymopathy in human, affecting over 400 million people in the world.
(Suofu Qin- Association of Glucose-6-Phosphate Dehydrogenase Deficiency with Ocular Diseases)
Last date updated on June, 2014