Artificial cofactor regeneration with an iron(III)porphyrin as NADH-oxidase mimic in the enzymatic oxidation of l-glutamate to α-ketoglutarate

In this contribution the use of an artificial in situ-cofactor regeneration with [Fe(III)TSPP]Cl for enzymatic amino acid oxidation, exemplified for the l-glutamate dehydrogenase-catalyzed synthesis of α-ketoglutarate from sodium l-glutamate, is reported. In comparison of two l-glutamate dehydrogenases, the one isolated from Clostridium difficile turned out to be the preferred enzyme. At a substrate concentration of 15 mM of l-glutamate in situ-cofactor regeneration using [Fe(III)TSPP]Cl as an “artificial NADH-oxidase” proceeded smoothly, leading to up to >99% overall conversion and 88% conversion related to the formation of α-ketoglutarate after 24 h. At an increased concentration of 50 mM of l-glutamate, a somewhat decreased conversion of 43% was observed (which, however, corresponds to a nearly doubled volumetric productivity of 3.95 g/(L d) compared to the experiments at 15 mM). Thus, the iron complex [Fe(III)TSPP]Cl turned out to be capable to be used for cofactor regeneration of the cofactor NAD+ for enzymatic amino acid oxidation.