Interaction of palladium(II) and platinum(II) complexes with microperoxidase-11 studied by electrospray mass spectrometry and MS/MS analysis.

Abstract

Interactions of cis-[Pd(en)(H(2)O)(2)](2+) (en, ethylenediamine) and cis-[Pt(NH(3))(2)(H(2)O)(2)](2+) with microperoxidase-11 (MP-11) in a molar ratio of 1:1 or 2:1 at pH 1.4 were investigated via electrospray mass spectrometry and MS/MS analysis at room temperature and at 40 degrees C with an incubation time of 2 or 3 days. The composition of the Pd(II)- and Pt(II)-anchored MP-11 was confirmed on the basis of the precise molecular mass and the simulated isotope distribution pattern. MS/MS analysis revealed that the Pd(II) center anchored to the side chain of Cys7 as Pd(II) and MP-11 were mixed in an equimolar ratio and to side chains of Cys7 and Cys4 as Pd(II) and MP-11 mixed in a 2:1 molar ratio. When Pt(II) and MP-11 were mixed in a 2:1 molar ratio, Pt(II) first anchored to the side chain of Cys7, and then to the side chain of Cys4 with time. The initial coordination of Pd(II) and Pt(II) to the side chain of Cys7 is the essential step for the Pd(II)- and Pt(II)-promoted cleavage of the His8-Thr9 bond in MP-11. These results support the hypothesis that the Pd(II)-mediated cleavage of the His18-Thr19 bond in cytochorome c is due to the identical binding mode.