Energy-Transducing Reaction in Biologyical Members. III. A Model of the Sodium Pump and Its Possible Relevance to Some Other Active Transport Processes

Abstract

A model of a sodium pump is presented which utilizes an alkali metal carrier in the form of a polypeptide "spring" containing about four consecutive phos-phatidylserine residues bound to lipid molecules embedded as a bilipid, rubber-like structure, attached to the matrix of a biological membrane. Electrostatic repulsive forces between the anions of the spring and osmosis, which are opposed by the elasticity of the bilipids, tend to maintain it in an expanded configuration of restricted dimensions, in which hydrated Na+ is preferred to K+ as a diffuse ionic atmosphere. Compression of the spring forms a helical structure in which unhydrated K+ is preferred to Na+ and is solvated by the oxygen atoms of carbonyl (or ether) groups within the peptide and the lipid.