DO PROTEINS DENATURE DURING DROPLET EVOLUTION IN ELECTROSPRAY-IONIZATION

The experiments described in this paper were designed to address the q uestion of whether proteins undergo denaturation on the millisecond ti mescale of the phase transition in electrospray ionization. The experi ments show that it is relatively difficult to induce a change in charg e in selected proteins by the application of heat to electrosprayed dr oplets during their transfer from atmospheric pressure to the vacuum o f the mass spectrometer. These findings indicate that the net heat tra nsfer to the droplets is insufficient for denaturation given the short lifetime of the droplets in the heated tube (0.6 ms or less) and prov ide a partial explanation as to why the charge distribution characteri stic of a protein in equilibrium in solution is to some extent preserv ed into the gas phase. Our findings lead us to suggest general guideli nes for improving the information about solution protein conformation and non-covalent associations obtained by electrospray ionization mass spectrometric measurements. (C) 1997 Elsevier Science B.V.