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Abstract
Two isoenzymes of glutamate dehydrogenase located in the cytoplasmic fraction of Nitrobacter agilis were specific for NAD+ and NADP+, respectively. The NAD+-dependent enzyme functioned in both directions, i.e. amination and deamination, whereas the NADP+ enzyme was primarily for the amination of 2-oxoglutarate to glutamate. The NADP+ enzyme was purified 52-fold (free of the NAD+ enzyme) by affinity chromatography on 2′,5′-ADP Sepharose 4B, and some of its properties studied. Substrate activation of the amination reaction of the NADP+ enzyme was observed with NH+ 4 and NADPH. A comparison is made of the properties of the purified NADP+ enzyme from Nitrobacter agilis and Nitrosomonas europaea. The possible roles of two isoenzymes of glutamate dehydrogenase in Nitrobacter agilis are discussed.
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