Glucose 6-phosphate dehydrogenase variants: a unique variant (G6PD Kobe) showed an extremely increased affinity for galactose 6-phosphate and a new variant (G6PD Sapporo) resembling G6PD Pea Ridge.

Abstract

Two new glucose 6-phosphate dehydrogenase (G6PD) variants associated with chronic nonspherocytic hemolytic anemia were discovered, G6PD Kobe was found in a 16-year-old male associated with hemolytic crisis after upper respiratory infection. The enzyme activity of the variant was about 22% of that of the normal enzyme. The main enzymatic characteristics were slower than normal anodal electrophoretic mobility, high Km G6P, increased thermal-instability, an acidic pH optimum, and an extremely increased affinity for the substrate analogue, galactose 6-phosphate (Gal-6P). G6PD Sapporo was found in a 3-year-old male associated with drug-induced hemolysis. The enzyme activity was extremely low, being 3.6% of normal. In addition, this variant showed high Ki NADPH and thermal-instability. G6PD Kobe utilized the artificial substrate Gal-6P effectively as compared with the common natural substrate, glucose 6-phosphate. In G6PD Sapporo, NADPH could not exert the effect of product inhibition. The structural changes of these variants are expected to occur at the portions inducing conformational changes of the substrate binding site of the enzyme.