Specificity of coenzyme analogues and fragments in promoting or impeding the refolding of clostridial glutamate dehydrogenase

Apparent negative co-operativity and substrate inhibition in overexpressed glutamate dehydrogenase from Escherichia coli

The gene for Escherichia coli glutamate dehydrogenase (EcGDH) has been overexpressed, and a simplified purification procedure afforded greatly increased yields of c. 40 mg pure EcGDH L(-1) culture. EcGDH was unstable at a low concentration in plastic tubes, but stabilization measures allowed a robust kinetic characterization. Contrary to past reports, EcGDH deviates from Michaelis-Menten kinetics, exhibiting apparent mild negative co-operativity with both l-glutamate and NADP+, with Hill coefficients of 0.90 and 0.92, respectively. NADPH yielded simple Michaelis-Menten kinetics but both 2-oxoglutarate and NH4+ showed substrate inhibition. pH optima were 9 for oxidative deamination and 8 for reductive amination.