Glutamate dehydrogenase mutants

Melo-Oliveira, R., Oliveira, I. C., and Comzzi, G. M. (1996). Arabidopsis mutant analysis and gene regulation define a nonredundant role for glutamate dehydrogenase in nitrogen assimilation. Proc. Natl. Acad. Sci. U.S.A. 93, 4718-4723. 

Figure 3-5. Temperature profile (A) and thermostability (B) of glutamate dehydrogenase from T. kodakaraensis KOD1 and its mutants. Data ofthe wild-type enzyme (circles), the T138E mutant protein (squares), and the E158Q mutant protein (triangles) are shown.

Drillien, R., Aigle, M., and Lacroute, F. (1973). Yeast mutants pleiotropically impaired in the regulation of the two glutamate dehydrogenases. Biochem. Biophys. Res. Commun. 53, 367-372. 

Normal strains of B. subtilis possess an NAD-dependent L-alanine dehydrogenase and are devoid of either NAD-GDH or NADP-GDH (29,236). am+ mutants of this species are known which contain a fairly active NADP-GDH and lack demonstrable alanine dehydrogenase activity (29,236), and it has been suggested that there is conversion of the alanine dehydrogenase to an enzyme with glutamate dehydrogenase activity by mutations induced by nitrous acid (237). 

In 1980, Miflin and Lea pointed out that much of the information on biochemical pathways has arisen from the use of mutants of bacteria and yeast larking key enzymes. They complained at the time that no mutants of higher plants were available in the ammonia assimilation pathway. A glance at Table I clearly indicates that a number of such mutants are now available. In addition mutants of maize with low (but not zero) levels of glutamate dehydrogenase have also been studied (Rhodes et ai, 1989). 

An understanding of the molecular basis for regulation of isocitrate dehydrogenase by phosphorylation was facilitated by X-ray crystallography of the phosphorylated enzyme in complex with isocitrate. The crystal structures of mutants of the enzyme in which SerllS had been exchanged for aspartate or glutamate were also solved (Hurley et al., 1990). The structure of the enzyme in complex with the substrate isocitrate revealed the phophorylation site to be localized near isocitrate. SerllS itself binds the substrate directly via a H-bond with the O of isocitrate (fig. 2.13). 

Among the fatty acid oxidation disorders, medium-chain acyl-CoA dehydrogenase deficiency (MCAD) is the most common and its frequency is similar to that of phenylketonuria. The disorder can be identified by mutant alleles and some key abnormal metabolites. An A G transition mutation occurs at position 985 of MCAD-cDNA in about 90% of cases. This mutation leads to replacement of lysine with glutamate at position 329 (K329E) of the polypeptide. 

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