Gas-phase dissociation of hemoglobin

The collisionally induced gas-phase dissociation of protein assemblies of hemoglobin has been investigated. In particular, the gas-phase disassembly of the holo-hetero-dimers and the holo-tetramers of bovine, porcine, and human hemoglobin have been studied. The holo-hetero-dimer ions dissociate primarily in apo-alpha -chains and holo-beta -chains, whereby the apo-alpha -chain ions accommodate more than a fair share of the initial charges present on the precursor ions. Comparing the collision-activated dissociation tandem mass spectrometry of three holo-tetramer assemblies one of the most important findings is that also these ions dissociate predominantly into the alpha -chain monomer concomitant with the alpha beta (2) trimer, whereby the alpha -chain monomer retains primarily 0 or 1, and the trimer 2-4 heme groups. Again the apo-a-chain ions accommodate more than a fair share of the initial charges, sometimes even more than the much larger alpha beta (2) trimer. The disparate charge distribution following the dissociation is in agreement with previous observations on other protein assemblies, and may to some extent be explained by assuming a charge-droplet fission model. Some significant differences are observed in the gas-phase disassembly of the hemoglobin complexes originating from the three different species. It is thought that these differences originate from differences in the gas-phase structures of these assemblies. The observed gas-phase dissociation patterns are in sharp contrast to the known solution-phase behaviour, providing a further indication that caution has to be taken when relating gas-phase data to solution-phase properties. (C) 2001 Elsevier Science B.V.