Or this phenomenon is definitely an ammoniadependent substrate amination activity of HisFCg in vivo (Fig. 1). Our findings support this theory, considering the fact that hisFCg is in a position to complement both, a hisF along with a hisH deletion, in E. coli (R.K. Kulis-Horn and P. Humbert, unpubl. obs.). The other possibility, a glutamine amidotransferase activity currently present in the HisF protein like observed in the monomeric IGP synthase HIS7 from Saccharomyces cerevisiae (Kuenzler et al., 1993), appears unlikely. HisFCg is only from the size of HisFEc and doesn’t exhibit any sequence similarities to known amidotransferases. The overexpression of hisHCg is in a position to complement a hisH deletion in E. coli, demonstrating that the hisHCg gene product is functional even though not required in C. glutamicum (Jung et al., 1998). So far, no other IGP synthase has been reported getting capable to catalyse the fifth step of histidine biosynthesis without the need of glutamine amidotransferase activity in vivo. These findings are extremely interesting particularly within the view on the biotechnological application of C. glutamicum as histidine producer, since histidine production in this organism seems to become independent of glutamine biosynthesis.2013 The Authors. Microbial Biotechnology published by John Wiley Sons Ltd and Society for Applied Microbiology, Microbial Biotechnology, 7, 5Histidine in C. glutamicum Imidazoleglycerol-phosphate dehydratase (HisB) The imidazoleglycerol-phosphate dehydratase catalyses the sixth step of histidine biosynthesis. The enzyme dehydrates IGP as well as the resulting enol is then ketonized non-enzymatically to imidazole-acetol phosphate (IAP) (Alifano et al., 1996). In S. typhimurium and E. coli this step is catalysed by a bifunctional enzyme comprising both, the imidazoleglycerol-phosphate dehydratase activity and also the histidinol-phosphate phosphatase activity, catalysing the eighth step of biosynthesis (Loper, 1961; Houston, 1973a). In these two organisms the bifunctional enzyme is encoded by the his(NB) gene, comprising phosphatase activity in the N-terminus in the encoded protein and dehydratase activity in the C-terminus (Houston, 1973b; Rangarajan et al., 2006). There’s proof that this bifunctional his(NB) gene results from a rather current gene fusion event within the g-proteobacterial lineage (Brilli and Fani, 2004).Obeticholic acid In eukaryotes, archaea and most bacteria the two activities are encoded by separate genes (Fink, 1964; le Coq et al., 1999; Lee et al., 2008). This is also true for C. glutamicum, with IGP dehydratase becoming encoded by hisB and histidinol-phosphate phosphatase by hisN (Mormann et al., 2006; Jung et al., 2009). Histidinol-phosphate aminotransferase (HisC) The seventh step of histidine biosynthesis may be the transamination of IAP to L-histidinol phosphate (Hol-P) employing glutamate as amino group donor (Alifano et al.Idelalisib , 1996).PMID:23910527 This step is catalysed by the pyridoxal 5-phosphate (PLP) dependent histidinol-phosphate aminotransferase in C. glutamicum (Marienhagen et al., 2008). Like HisC from E. coli and S. typhimurium (Winkler, 1996), native HisCCg acts as a dimer (Marienhagen et al., 2008). Kinetic parameters of HisCCg have been determined only for the backreaction converting Hol-P and a-ketoglutarate into IAP and L-glutamate. The enzyme exhibits a Km value for Hol-P of 0.89 0.1 mM, a kcat worth of 1.18 0.1 s-1 as well as a specific activity of 2.8 mmol min-1 mg-1 (Marienhagen et al., 2008). Interestingly, HisCCg shows also activity together with the precursors of leucine and aromatic amino acids in in vitro.