Mannitol kinase

Unphosphorylated functioning according to Fig. 5 catalyzes facilitated diffusion of mannitol across the membrane. The same process has been reported for purified II reconstituted in proteoliposomes [70]. The relevance of this activity in terms of transport of mannitol into the bacterial cell is probably low, but it may have important implications for the mechanism by which E-IIs catalyze vectorial phosphorylation. It would indicate that the transmembrane C domain of Il is a mannitol translocating unit which is somehow coupled to the kinase activity of the cytoplasmic domains. We propose that the inwardly oriented binding site which is in contact with the internal water phase (Ecyt Mtl, see Fig. 5) is the site from where mannitol is phosphorylated when transport is coupled to phosphorylation. Meehan-... 

Arima, H., Yamamoto, N., Sobue, K. etal. Hyperosmolar mannitol simulates expression of aquaporins 4 and 9 through a p38 mitogen-activated protein kinase-dependent pathway in rat astrocytes. /. Biol. Chem. 278 44525-44534,... 

In certain conditions, when the cell makes use of other coenzyme reoxidation systems, the acetate kinase catalyzes a reaction that leads to the formation of acetate from acetyl-P. This reaction simultaneously recuperates the bond energy of the P group of acetyl-P by the synthesis of an ATP molecule. In this case, the coenzyme reoxidation systems activate NADH or NADPH oxidases, when the cells are in aerobiosis or reduction reactions such as the transformation of fructose into mannitol. When acetyl-P leads to the formation of acetate, there is a definite energetic advantage. A supplementary ATP molecule is formed for each hexose molecule transformed. 

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