Mannitol-6-phosphate dehydrogenase

Wisselink, H. W., Mars, A. E., van der Meer, P., Eggink, G, and Hugenholtz, J. 2004. Metabolic engineering of mannitol production in Lactococcus lactis influence of overexpression of mannitol-1-phosphate dehydrogenase in different genetic backgrounds. App. Environ. Microbiol., 76,4286 1292. 

Figure 11.1 Proposed pathway for hex-ose metabolism of homofermentative LAB (1) and (2) phosphoenolpyruvate (PEP)-dependent sugar phosphotransferase system (PTS) (3) mannitol-specific PTS (4) phospho-glucose isomerase (5) mannitol-1-phosphate dehydrogenase (6) mannitol-1-phosphatase (7) 6-phosphofructokinase (8) fructose-diphosphatase (9) fructose-1,6-diphosphate aldolase (10) triosephosphate isomerase (11) glyceraldehyde-3-phosphate dehydrogenase...

In this scheme, reaction (4), leading to the regeneration of cytosine triphosphate from ATP can be accomplished by nucleoside diphosphokinase 100, 101). Reactions (1) to (3) are unknown, per se however, known analogous mechanisms can be cited. Reaction (1) would be like mannitol 1-phosphate dehydrogenase fotmd in a number of bacteria 102-104) which... 

L.A., Nadal, L, Monedero, V. et al (2010) Sorbitol production om lactose by engineered Lactobacillus casei deficient in sorbitol transport system and mannitol-l-phosphate dehydrogenase. Appl. Microbiol Biotechnol, 85, 1915-1922. 

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 ... 

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. 

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