Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

It is now possible to transfer large protein complexes intact into the gas phase using nano-electrospray ionisation (ESI) and to investigate their stoichiometry in a mass spectrometer. Using as a model assembly the noncovalent 14mer (ca. 800 kDa) of the chaperonin GroEL from Escherichia coli we show that the measured mass of the assembly is higher than expected from the sum of the components and explore parameters of ion activation that affect this 'noncovalent mass shift'. Under optimal desolvation conditions the measured mass is ∼0.5% greater than the calculated value indicating that part of the solution environment remains attached to these ions during phase transfer. The origin of this noncovalent mass shift is explored using tandem mass spectrometry experiments. Collisional activation of the 65+ charge state of the GroEL 14mer indicates the presence of up to 100 solvent/buffer molecules, both positively and negatively charged, which are stripped during CID in the gas-filled collision cell. At high collision energies, asymmetric dissociation into highly charged monomer and 13mer complexes takes place revealing the subunit composition of the assembly. Under these conditions the noncovalent mass shift is significantly reduced (<0.04%) demonstrating the utility of this tandem approach for mass measurement of biomolecules in the gas phase. © 2004 Elsevier B.V. All rights reserved.

Original publication




Journal article


International Journal of Mass Spectrometry

Publication Date





25 - 32