Affiliation:
1. Department of Chemistry and Biochemistry National Chung Cheng University Chia‐Yi 621 Taiwan
2. Center for Nano Bio‐Detection Technology Research National Chung Cheng University Chia‐Yi 621 Taiwan
Abstract
AbstractThis paper reports notable observations regarding the ion charge states of thermally stable cytochrome c, generated using an alternating current (AC) electrospray ionization (ESI) device. An AC ESI sprayer entrains low‐mobility ions to accumulate at the meniscus cone tip prior to the ejection of detached aerosols to produce analyte ions. Therefore, as the solvent acidity varies, protein ions entrained in the AC cone tip are found to change conformation less significantly compared with those in the direct current (DC) cone. We acquired the AC ESI mass spectra of cytochrome c at pH range from 2 to 4. Unlike the DC ESI mass spectra showing clear conformation changes due to denaturing, the AC spectra indicated that only partial denaturing occurs even at extremely acidic pH 2. More native cytochrome c in lower charge states therefore remained. Moreover, with a solvent mixture of aqueous buffer and acetonitrile (70:30), partially denatured cytochrome c was still preserved at pH 2 by using AC ESI. Completely denatured proteins are observed at pH 2 by using DC ESI.