Dissociation of heme-globin complexes by blackbody infrared radiative dissociation: Molecular specificity in the gas phase?

• Published in: Journal of the American Society for Mass Spectrometry 1997-05, Vol.8 (5), p.519-524
• Main Authors: Gross, Deborah S., Zhao, Yuexing, Williams, Evan R.
• Format: Article
• Language: English
• Subjects: Acidification; Activation energy; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Blackbody; Energy of dissociation; Fundamental and applied biological sciences. Psychology; Hemoglobin; Hemoproteins; Ionization; Ions; Mass spectrometry; Metalloproteins; Myoglobins; Process parameters; Proteins; Temperature dependence; Thermal dissociation
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1016/S1044-0305(97)00010-X

The temperature dependence of the unimolecular kinetics for dissociation of the heme group from holo-myoglobin (Mb) and holo-hemoglobin α-chain (Hb-α) was investigated with blackbody infrared radiative dissociation (BIRD). The rate constant for dissociation of the 9 + charge state of Mb formed by electrospray ionization from a “pseudo-native” solution is 60% lower than that of Hb-α at each of the temperatures investigated. In solutions of pH 5.5–8.0, the thermal dissociation rate for Mb is also lower than that of HB-α (Hargrove, +M. S. et al. J. Biol. Chem. 1994, 269, 4207–4214). Thus, Mb is thermally more stable with respect to heme loss than Hb-α both in the gas phase and in solution. The Arrhenius activation parameters for both dissociation processes are indistinguishable within the current experimental error (activation energy 0.9 eV and pre-exponential factor of 10 8–10 s −1). The 9+ to 12+ charge states of Mb have similar Arrhenius parameters when these ions are formed from pseudo-native solutions. In contrast, the activation energies and pre-exponential factors decrease from 0.8 to 0.3 eV and 10 7 to 10 2 s −1, respectively, for the 9+ to 12+ charge states formed from acidified solutions in which at least 50% of the secondary structure is lost. These results demonstrate that gas-phase Mb ions retain clear memory of the composition of the solution from which they are formed and that these differences can be probed by BIRD. (J Am Soc Mass Spectrom 1997, 8, 519-524)