Glucose-6-phosphate dehydrogenase from Dicentrarchus labrax liver: kinetic mechanism and kinetics of NADPH inhibition |
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| Authors: | J M Bautista A Garrido-Pertierra G Soler |
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| Institution: | Departamento de Bioquímica y Biologia Molecular y Genética, Universidad de Extremadura, Facultad de Veterinaria, Cáceres, Spain. |
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| Abstract: | 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. |
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