Adsorption of a macromolecule to a charged surface

The adsorption of a charged macromolecule to a charged surface under the influence of a weak electrostatic attraction is investigated. The probability density P(x,N) to find the end point of a molecule with N monomer units at distance x from the surface is calculated analytically. In the limit N to infinity this function shows a phase transition at a critical value ( theta c ) of the adsorption energy in units if k B T: for theta > theta c P(x,N) is peaked near the surface and the molecule is effectively adsorbed to the surface; for theta < theta c the heat motion is strong enough to remove the molecule from the surface and P(x,N) is effectively constant throughout the whole available volume. A possible role of such conformational phase transitions in the regulation of cellular metabolism is briefly commented on.