ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 36, Number 4
JKCSEZ 36(4)
August 20, 1992 

The conformations of hexapeptides, their complexation with alkali cations and the inhibition of the cation transport by 5,5-diphenylhydantoin(DPH) were studied theoretically using ECEPP/2 and MM2 force field. Several low energy conformations of uncomplexed cyclic hexapepides are obtained, and they adopt compact conformations in which most amide hydrogens form intramolecular hydrogen bond to amide carbonyl oxygens. The complexation energy of the peptide with Na+ ion and DPH is -60 kcaal/mol and -18 kcal/mol, respectively. However, no suitable cavity to bind metal cation exists for the local minima of the peptide, and the internal energy of the uncomplexed hexapeptide having cavity is higher than that of the uncomplexed global minimum of this work by 10 kcal/mol. Also, one of the most important amino acid residue to bind DPH is Glycine, and this can explain experimental observation that the replacement of Gly by Sarcosine (N-methyl Glycine) reduce the inhibition ability of the cation transport.