Orientation of substrate and two conformations of lactose permease.
The accessibility of substrate bound to lactose permease of Escherichia coli was investigated by using the fluorescent substrate dansyl galactoside and a membrane-impermeable fluorescence quencher. To determine the orientation of bound substrate, both cells and inside-out vesicles were used. The substrate is oriented with the dansyl group toward the cytoplasm and the galactoside group toward the periplasm. Only half of the dansyl groups are accessible to quencher, irrespective of their orientation. This is interpreted as evidence for two different conformations of lactose permease, one with the binding site open to the cytoplasm and closed to the periplasm and vice versa for the other state.[1]References
- Orientation of substrate and two conformations of lactose permease. Dornmair, K., Jähnig, F. Biochemistry (1988) [Pubmed]
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