[Pt(dien)]2+ migrates intramolecularly from methionine S to imidazole Nepsilon2 in the peptides H-His-Gly-Met-OH and Ac-His-Ala-Ala-Ala-Met-NHPh.
The pH- and time-dependent reaction of [Pt(dien)(H2O)]2+ with the methionine- and histidine-containing peptides H-His-Gly-Met-OH and Ac-His-Ala-Ala-Ala-Met-NHPh at 313 K has been investigated by HPLC and NMR spectroscopy. For both peptides, initial relatively rapid formation of the kinetically favoured methionine S-bound complex is followed by slow intramolecular migration of the [Pt(dien)]2+ fragment to imidazole Nepsilon2 (or, in the case of H-His-Gly-Met-OH, to a much lesser extent to the competing imidazole Ndelta1) of the histidine side chain over a period of 500 h. Time-dependent studies for the pentapeptide at pH 8.0 demonstrate that this isomerization can take place by either direct S-->Nepsilon2 migration or by a two-step mechanism involving initial Nepsilon2 coordination of a second [Pt(dien)]2+ fragment and subsequent cleavage of the orginal Pt-S bond in the resulting dinuclear complex. The rate of kappaS/kappaNepsilon2 isomerization is markedly reduced on lowering the pH to 5.1.
Hahn
M
M
Lehrstuhl für Analytische Chemie, Ruhr-Universität Bochum, Germany.
Wolters
D
D
Sheldrick
W S
WS
Hulsbergen
F B
FB
Reedijk
J
J
D000595:Amino Acid Sequence; D001667:Binding, Competitive; D002851:Chromatography, High Pressure Liquid; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008715:Methionine / Q000737:chemistry* / Q000378:metabolism; D009944:Organoplatinum Compounds / Q000737:chemistry* / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism*; D010984:Platinum / Q000737:chemistry* / Q000378:metabolism
D007093:Imidazoles; D009944:Organoplatinum Compounds; D010455:Peptides; C121932:diaquadiethylenediamineplatinum(II); D010984:Platinum; C029899:imidazole; D008715:Methionine