Proposed sucrose metabolism in L. lactis NZ9800/NZ9841 overproducer strain MDH isolated from Leuconostoc mesenteroides. (a), phosphorylation of fructose into fructose 6-phosphate by fructokinase (b), export and the subsequent import of fructose by the fructose PTS (PTSfru) or the mannose PTS (PTSman) (c), and the conversion of fructose into glucose by a xylose isomerase-like enzyme activity (d). Mannitol is exported by an unknown mechanism, and is possibly re-utilized by the mannitol PTS (PTSmtl) [18]. (e) Mannitol uptake mechanism. Enzyme abbreviations: sucrose 6-phosphate hydrolase (S6PH), mannitol dehydrogenase (MDH), fructokinase (FK), glucokinase (GK), 1-phosphofructokinase (1-PFK), xylose isomerase (XI), phosphotransferase system (PTS).