Acetonitrile as a Buffer Additive for Free Zone Capillary Electrophoresis Separation and Characterization of Maize (Zea mays L.) and Sorghum (Sorghum bicolor L. Moench) Storage Proteins

Abstract

An improved method for separating and characterizing maize (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) storage proteins by free zone capillary electrophoresis (FZCE) was developed. Previous electrophoretic methods for analyzing these proteins required high concentrations of urea to maintain protein solubility during separation. To overcome disadvantages of urea, we developed a FZCE method that mimicked reversed-phase high-performance liquid chromatography (RP-HPLC) in that it used high levels of acetonitrile (ACN) at low pH. The optimized FZCE buffer system consisted of 80 mM phosphate-glycine buffer, nominal pH 2.5, containing 60% ACN and a cellulose derivative to dynamically coat capillary walls. Resolution was similar to or higher than that previously achieved by FZCE buffers utilizing 8 M urea as a buffer additive. ACN concentrations of at least 50% were necessary to achieve acceptable separations; this ACN concentration is approximately that necessary to extract these storage proteins. ACN was equally effective as traditional ethanol solvents and 8 M urea for solubilizing maize and sorghum proteins. The ACN-based FZCE buffer system gave high repeatability (<0.3% relative standard deviation, measured over 15 consecutive injections) for migration time. Subclasses of maize and sorghum storage proteins were identified, and genotypes of each cereal were successfully differentiated using ACN-containing buffers. This FZCE method may be applicable for the analysis of other hydrophobic proteins without the use of urea.