The first cytoplasmic loop of the mannitol permease from Escherichia coli is accessible for sulfhydryl reagents from the periplasmic side of the membrane.

The mannitol permease (EII(Mtl)) from Escherichia coli couples mannitol transport to phosphorylation of the substrate. Renewed topology prediction of the membrane-embedded C domain suggested that EII(Mtl) contains more membrane-embedded segments than the six proposed previously on the basis of a PhoA fusion study. Cysteine accessibility was used to confirm this notion.