Ammoniagenes

Processes employing Toru/opsis yjlinus (55), Hansenu/apoljmorpha (56), Brevibacterium ammoniagenes (57), A.chromobactor butrii (58), Micrococcus lactis (59), Streptomjces testaceus (60), and others have also been patented. These procedures yield, at most, several hundred milligrams of riboflavin per Hter. 

Both dietary and endogenous ammoniagenic substrates are removed from the intestinal lumen by the osmotic cathartic action of nonabsorbable disaccharides such as lactulose and lactitol. These compounds are currently the main therapeutic agents for chronic HE. The efficacy of oral lactulose for the treatment of HE has been established in controlled trials [41-43]. Besides having a cathartic effect, lactulose lowers the colonic pH as a result of the production of organic acids by bacterial fermentation. The decrease in pH creates an environment that is hostile to the survival of urease-producing intestinal bac-... 

Scheme 5.7 Combination of three bacterial strains for the production of globotriose (13) with regeneration of UDP-Gal [40]. Combination of C. ammoniagenes DN510 (A), E. coli NM 522 pNT25/pNT32 (B) and E. coli NM522 pGT5 (C).

This process has been operated successfully by the Tanabe Seiyaku Co. in Japan since 1973. Similar processes have since been commercialised by other companies, such as the Kyowa Hakko Co., often using different immobilisation methods such as polyurethane. The same iimnobilized cell approach has also been used by Tanabe since 1974 in their coimnercial process for the production of L-malic acid from fumarate using the hydratase activity of Brevibacterium ammoniagenes cells. 

Process development with Brevibacterium ammoniagenes (introduced in 1974), similarly to the development in the i-aspartate process led to 25-fold improvements, mainly through use of a Brevibacteriumflavum strain immobilized on ic-carrageenan gel with polyethyleneimine (PEI) crosslinker, so that a half life of 310 days at 37°C has been achieved. 

The first bona fide MnRNR, isolated from Corynebacterium (formerly Brevibacterium) ammoniagenes, was reported about 10 years ago [122], The MnRNR R1 protein is monomeric (dimeric in E. coli) [123]. A dinuclear Mnm—0—Mnm unit was believed to be present at its active site (cf. oxidized E. coli RNR), and its sensitivity to hydroxyurea (a radical scavenger) suggested a mechanism similar to that of its iron counterpart. However, no tyrosyl radical EPR signal was observed from the MnRNR, casting doubts about the redox role of the manganese center [118], Very recently, however, a stable EPR signal, which is inhibited by hydroxyurea and correlates directly with enzymatic activity, has been detected [124],... 

A lesion of the Krebs Cycle caused by ammonia has been proposed by Bessman and Bessman as the mechanism of ammoniagenic coma and... 

Butler M, Christie A (2004), Adaptation of mammalian cells to non-ammoniagenic media, Cytotechnology 15 87-94. 

Hassell T, Butler M (1990), Adaptation to non-ammoniagenic media and selective substrate feeding lead to enhanced yields in animal cell culture, J. Cell Sci. 96 501-508. 

The above reaction was known many years ago (Komberg, 1950 Wang and Kaplan, 1954) and found both in procaryotes and eucaryotes. In Brevibacterium ammoni-agenes (Murata et al., 1979), Micrococcus luteus and Corynebacterium ammoniagenes (Fillipovich et al., 2000) phosphorylation of NAD using PolyP as a phosphate donor was revealed ... 

V. L. Kozel tsev, S. S. Debov and N. I. Votrin (1969). The role of inorganic polyphosphates in the formation of adenyl nucleotides in a culture of Brevibacterium ammoniagenes (in Russian). Vopr. Med. Khim., 5, 602-614. 

K. Murata, J. Kato and I. Chibata (1979). Continuous production of NADP by immobilized Brevibacterium ammoniagenes cells. Biotechnol. Bioeng., 21, 887-895. 

A similar process is also used for the production of L-malic acid from fumarate, in this case using a hydratase enzyme derived from Brevibacterium ammoniagenes. Another variation of the Tanabe technology involves the synthesis of L-alanine from L-aspartic acid through the use of immobilized whole cells (P dacunae) containing aspartate-decarboxylase. 

Fumarase. The development and use of this immobilized enzyme by Tanabe Seiyaku for production of L-malic acid is very similar to that of aspartase ( 3). Lysed Brevibacterium ammoniagenes or B. flavin cells are treated with bile acid to destroy enzymatic activity which converts fumarate to succinate. As with aspartase, the cells can be immobilized in polyacrylamide or k-carrageenan gels. Using a substrate stream of 1 M sodium fumarate at pH 7.0 and 37°C, L-malic acid of high purity has been produced since 1974 by a continuous, automated process (3,39) for example, using a 1000-L fixed-bed bioreactor, 42.2 kg L-malic acid per hour was produced continuously for 6 months. 

It was suggested, based on UV-visible and EPR spectroscopy, that the ribonucleotide reductase from Corynebac-terium ammoniagenes contains Mn rather than Fe in its native form. However, more recent crystallographic studies have shown that this protein is structurally identical to the native iron proteins and apparently does not contain a Mn active... 

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