Conformational studies of the N-acetyl-S-methyl- l-cysteinyl- l-histidylglycine methyl amide cation using the AM1 method

Abstract

Conformational studies of N-acetyl-S-methyl- l-cysteine (AcCysMe), the N-acetyl- l-histidylglycine cation([AcHis-Gly] +) and the N-acetyl-S-methyl- l-cysteinyl- l-histidylglycine methyl amide cation ([AcCysMe-His-Gly-NHMe] +) have been carried out using the AM1 semiempirical method. Three-dimensional energy surfaces of AcCysMe and [AcHis-Gly] + were obtained. The conformation of [AcCysMe-His-Gly-NHMe] + was computed using the combined optimum structures of AcCysMe and [AcHis-Gly] +(the acetyl group was deleted). From our calculations, the most stable conformer of the tripeptide exhibits a hydrogen bond between the carbonyl group of the glycine and the ring-NH + of the histidine moiety. This conformation is in accordance with that of a tripeptide chelate of palladium(II) proposed in one of our previous articles. These results provide direct evidence for the importance of the His18 residue of cytochrome c concerning the selective cleavage of cytochrome c promoted by palladium(II) complexes.