Fig 1.
Schematic overview of the two alternative pathways for lactose transport and metabolism in L. lactis. When internalized via the PTSLac (LacEF), lactose is phosphorylated and hydrolyzed by phospho-β-galactosidase (LacG); the glucose moiety enters glycolysis, while galactose 6-phosphate is degraded via the tagatose 6-P pathway (LacABCD). When lactose is internalized via the lactose-specific permease (LacY), unphosphorylated lactose is cleaved by β-galactosidase (LacZ), and the resulting galactose molecule enters the Leloir pathway (GalMKTE), while the glucose moiety is directed to glycolysis.