Surface electrostatic potentials on macromolecules in a monopole approximation: a computer program and an application to cytochromes.

A new tool for detg. and analyzing mol. electrostatic potentials (MEP) of very large biomols. is presented and illustrated. The MEP's are computed in a monopole approxn. with inclusion of inductive effects by a chain of computer programs (running even on small computers) based on net charges calcd. in a σ-π sepn. scheme according to the method of G. Del Re (1964). This method is applicable to virtually any macromol. and yields fairly reliable net charges. The use of MEP's in the study of reaction mechanisms as well as the solvent problem and use of ad hoc dielec. consts. are briefly discussed. Since MEP's are esp. well suited to the study of oxido-reaction mechanisms, the scope of the new program is illustrated on the maps of reduced and oxidized states of some monoheme cytochromes at their van der Waals frontiers. The results throw further light on the way in which the protein modulates the properties of the heme group