Electrospray ionization mass spectrometry and on-line capillary zone electrophoresis - mass spectrometry for the characterization of citrate synthase

The enzyme citrate synthase from E. coli is a protein with a molecular weig ht (M-r) of 47 885 Da (wild type). This enzyme has been studied extensively , and its amino acid sequence has been characterized. This model protein ha s been used in this work for development and validation of methods involvin g capillary electrophoresis (CE) and electrospray ionization mass spectrome try (ESI-MS). The nti, determinations were conducted using sample infusion ESI-MS, and the tryptic digestion products of wild-type citrate synthase we re characterized by on-line CE-ESI-MS coupled with a sheathless interface. On-line experiments were conducted on two different mass spectrometers, a Q uattro-LC triple quadrupole instrument equipped with a Z-Spray(TM) source ( Micromass), and a reflecting time-of-flight (TOF) mass spectrometer builtin -house in the Time-of-Flight Laboratory, Department of Physics, University of Manitoba. This is the first article to be written on the interfacing of a Z-Spray(TM) source with CE. Unmodified fused silica capillaries gold-coat ed sheathless interfaces were used. The an-line CE separations yielded theo retical plate numbers greater than 10(4) on average. Selected ion erectroph orograms (SIE) of the tryptic peptides recorded on the Quattro-LC displayed SIN ratios ranging from ca. 14 to 120 on raw data. These SIE enabled ident ification of each peptide. The use of reflecting time-of-flight mass spectr ometry (TOFMS) afforded mass resolution values of ca. 6000 (m/Delta m(FWHM) ), which enabled isotopic resolution of the peptide components. CE-ESI-MS a nd CE-ESI-TOFMS experiments enabled the generation of a complete tryptic ma p of citrate synthase.