Glucose-6-phosphate dehydrogenase from Dicentrarchus labrax liver: kinetic mechanism and kinetics of NADPH inhibition

• Published in: Biochimica et biophysica acta Vol. 967; no. 3; pp. 354 - 363
• Main Authors: Bautista, JoséM., Garrido-Pertierra, Amando, Soler, Germán
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.12.1988; Elsevier; North-Holland
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Bass; Biological and medical sciences; Chromatography, Gel; Chromatography, Ion Exchange; D labrax; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Glucose-6-phosphate dehydrogenase; Glucosephosphate Dehydrogenase - antagonists & inhibitors; Glucosephosphate Dehydrogenase - isolation & purification; Glucosephosphate Dehydrogenase - metabolism; Kinetic mechanism; Kinetics; Liver - enzymology; Mathematics; NADP - pharmacology; NADPH inhibition; Oxidation-Reduction; Oxidoreductases; NADPH inhibition; G6P, glucose 6-phosphate; Glucose-6-phosphate dehydrogenase; Kinetic mechanism; 6GPδL, 6-phosphoglucono-δ-lactone; D labrax; Vertebrata; Regulation(control); Enzyme; Pisces; Liver; Dicentrarchus labrax; Kinetics; Inhibition; NADP
• ISSN: 0304-4165; 0006-3002; 1872-8006; 1878-2434
• DOI: 10.1016/0304-4165(88)90098-0

The kinetic mechanism of the reaction catalyzed by glucose-6-phosphate dehydrogenase (EC 1.1.1.49) from Dicentrarchus labrax liver was examined using initial velocity studies,NADPH and glucosamine 6-phosphate inhibition and alternate coenzyme experiments. The results are consistent with a steady-state ordered sequential mechanism in which NADP + binds first to the enzyme and NADPH is released last. Replots of NADPH inhibition show an uncommon parabolic pattern for this enzyme that has not been previously described. A kinetic model is proposed in agreement with our kinetic results and with previously published structural studies (Bautista et al. (1988) Biochem. Soc. Trans. 16, 903–904). The kinetic mechanism presented provides a possible explanation for the regulation of the enzyme by the [NADPH]/[NADP +] ratio.