COLLISION CROSS-SECTIONS FOR PROTEIN IONS

A method for the determination of cross sections for gas-phase protein ions, based on the energy loss of ions as they pass through a collisi on gas, is described. A simple model relates the energy loss to the nu mber of collisions and hence the cross section. Results from a Monte C arlo model that support the validity of this approach are described. E xperimental cross sections are reported for motilin, ubiquitin, cytoch rome c myoglobin, and bovine serum albumin. Cross sections range from approximately 800 angstrom2 for motilin to approximately 14,000 angstr om2 for bovine serum albumin and generally increase with the number of charges on the ion. Cytochrome c ions from aqueous solution show some what smaller cross sections than ions formed from solutions of higher organic content, suggesting that the gas-phase ions may retain some me mory of their solution conformation.