PRIMARY TO QUATERNARY PROTEIN-STRUCTURE DETERMINATION WITH ELECTROSPRAY-IONIZATION AND MAGNETIC-SECTOR MASS-SPECTROMETRY

Electrospray ionization with a forward-geometry magnetic sector mass s pectrometer was used for collisionally activated dissociation studies of multiply charged polypeptides and for studying non-covalently bound protein systems. The high-resolution capabilities of a high-performan ce instrument allow the resolution of isotopic contributions for produ ct ions and molecular ion species. Determination of product ion charge states by this method reduces difficulties in the interpretation of p roduct ion mass spectra from multiply charged precursors, which are ge nerated either in the atmospheric pressure/vacuum electrospray interfa ce or in the collision chamber of the mass spectrometer. Extended tand em mass spectrometric experiments have the potential for sequencing la rger polypeptides. However, evidence for isomerization of gas-phase pr oduct ions from substance P and substance P analogues was observed, co mplicating the interpretation of product ion spectra. Non-covalent com plexes can also be studied by electrospray ionization magnetic sector MS. The higher m/z range of such an instrument is a major advantage fo r studying weakly bound systems, such as heme-protein systems (myoglob in, hemoglobin) and protein aggregates (concanavalin A), because of th eir,tendency to form complex ions with relatively low charge states.