Mannitol dehydrogenase

Several heterofermentative LAB produce mannitol in large amounts, using fructose as an electron acceptor. Mannitol produced by heterofermentative bacteria is derived from the hexose phosphate pathway (Soetaert et al., 1999 Wisselink et al., 2002). The process makes use of the capability of the bacterium to utilize fructose as an alternative electron acceptor, thereby reducing it to mannitol with the enzyme mannitol dehydrogenase. In this process, the reducing equivalents are generated by conversion of one-third fructose to lactic acid and acetic acid. The enzyme reaction proceeds according to (theoretical) Equation 21.1 ... 

Heterofermentative LAB have the capability to utilize high concentrations of fructose such that the mannitol concentration in the fermentation broth could reach more than 180g/L, which is enough to be separated from the cell-free fermentation broth by cooling crystallization. Lactic and acetic acids can be recovered by electrodialysis (Soetaert et al., 1995). The enzyme mannitol dehydrogenase responsible for catalyzing the conversion of fructose to mannitol requires NADPH (NADH) as cofactor. Thus, it is possible to develop a one-pot enzymatic process for production of mannitol from fructose if a cost-effective cofactor regeneration system can be developed (Saha, 2004). The heterofermentative LAB cells can be immobilized in a suitable support, and... 

Liu, S., Saha, B., and Cotta, M. 2005. Cloning, expression, purification, and analysis of mannitol dehydrogenase gene mtlK from Lactobacillus brevis. Appl. Biochem. Biotechnol., 121-124, 391 102. 

Martinez, G. H., Barker, A., and Horecker, B. L. 1963. A specific mannitol dehydrogenase from Lactobacillus brevis. J. Biol. Chem., 238,1598-1603. 

Saha, B. C. 2004. Purification and characterization of a novel mannitol dehydrogenase from Lactobacillus intermedius. Biotechnol. Prog., 20,537-542. 

Sasaki, Y., Laivenieks, M., and Zeikus, J. G. 2005. Lactobacillus reuteri ATCC 53608 mdh gene cloning and recombinant mannitol dehydrogenase characterization. Appl. Microbiol. Biotechnol., 68, 36-41. 

Reductions catalyzed by glycerol dehydrogenase, sorbitol dehydrogenase, mannitol dehydrogenase, and aldose reductases formation of polyols from carbohydrates. 

Sugar alcohols mannitol and xylitol are used as sweeteners [113]. Mannitol also has some medical uses [114]. Mannitol is produced in a single step from D-fructose by mannitol dehydrogenase. In one E. coli system, reducing power from formate was used and D-fructose was converted to mannitol with 84% molar yield and final titer about 66 g 1 [115]. 

Another dehydrogenase found in Acdobacter suboxydans requires that the substrate have the structure of one end of D-mannitol, and has been named D-mannitol dehydrogenase (XXV). The reaction occurs in the position indicated if one of the hydrogens of carbon 1 is replaced by a methyl group. A similar oxidation is catalyzed by an enzyme with no cofactor requirement. 

As stated previously, many heterofermentative lactic acid bacteria gain additional energy by converting acetyl phosphate to acetate instead of ethanol. Although an additional ATP can be produced, the cell requires regeneration of NAD, a process achieved using an alternative electron acceptor, fructose (Wisselink et al., 2002). The reduction of fructose to mannitol by lactic acid bacteria catalyzed by mannitol dehydrogenase is shown in Fig. 2.8. 

Metz B, de Vries RP, Polak S, Seidl V, Seiboth B (2009) The Hypocrea jecorina (syn. Trichoderma reesei) Ixrl gene encodes a D-mannitol dehydrogenase and is not involved in L-arabinose catabolism. FEBS Lett 17 1309-1313... 

Further structural diversification of FruA products has been investigated by enzymatic reduction to corresponding alditols using stereochemically complementary alditol dehydrogenases (Figure 5.40). Indeed, stereospecific (2S)- and (2R)-specific reduction of simple derivatives of o-fructose could be achieved by NADH-dependent catalysis of sorbitol dehydrogenase (EC 1.1.1.14) [209] or mannitol dehydrogenase (EC 1.1.1.67), respectively [26]. 

Mannitol dehydrogenase Fructose High Charged membrane 150000 99, 100, 101... 

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