An ENZYME that performs an essential function in the metabolism of CARBOHYDRATE. A deficiency in this enzyme – acronym G6PD – results in the breakdown of ERYTHROCYTES (HAEMOLYSIS), usually provoked by infections or certain drugs. The deficiency disorder is a hereditary condition in which the enzyme is absent. The condition is characterised by episodes of pallor, RIGOR and pain in the loin.(See FAVISM.)