Dissociation of heme from gaseous myoglobin ions studied by infrared multiphoton dissociation spectroscopy and Fourier-transform ion cyclotron resonance mass spectrometry

Abstract

Detachment of heme prosthetic groups from gaseous myoglobin ions has been studied by collision-induced dissociation and infrared multiphoton dissociation in combination with Fourier-transform ion cyclotron resonance mass spectrometry. Multiply charged holomyoglobin ions (hMb(n+)) were generated by electrospray ionization and transferred to an ion cyclotron resonance cell, where the ions of interest were isolated and fragmented by either collision with Ar atoms or irradiation with 3 mu m photons, producing apomyoglobin ions (aMb(n+)). Both charged heme loss (with [Fe(III)-heme](+) and aMb((n-1)+) as the products) and neutral heme loss (with [Fe(II)-heme] and aMb(n+) as the products) were detected concurrently for hMb(n+) produced from a myoglobin solution pretreated with reducing reagents. By reference to E-a=0.9 eV determined by blackbody infrared radiative dissociation for charged heme loss of ferric hMb(n+), an activation energy of 1.1 eV was deduced for neutral heme loss of ferrous hMb(n+) with n=9 and 10. (c) 2006 American Institute of Physics.