Charge anisotropy across biological membranes: evidence and implications.

Membrane proteins exhibit charge anisotropy across the bilayer with the vector positive inwards. The proton pumps, primary or secondary, which have been examined as a subset of these membrane proteins, also reveal charge anisotropy based on their sequence data. The direction of the anisotropy appears to satisfy the observed directional gradient of protons mediated by these proteins. A correct description of transport requires attention to local as well as field effects of the charge anisotropy of membrane proteins.