SEMIEMPIRICAL HARTREE-FOCK CALCULATIONS ON THE MECHANISM OF ENNIATIN-B MEDIATED TRANSPORT OF SODIUM-IONS

The passage of sodium ions through enniatin B is studied by the CNDO method. Electronic dissociation energy of the enniatin B-Na+ complex in water is 0.496 au for the open form (0.397 au for the closed form). The open complex is found to be more stable than the closed one in water. The dissociation energy changes when counterions representing charged heads of phospholipids are placed around the ionophore. Variation of counterion charges leads to different possibilities for the transport of Na+ across a lipid membrane. These are (i) no transport, (ii) transport through channels and (iii) transport of the ion-ionophore complex. A pH dependence that relies on the nature of counterion charges is predicted for the transport