| Abstract
| - A two-dimensional liquid phase separation of proteinsfrom whole cell lysates coupled on-line to an electrospray-ionization time-of-flight (ESI-TOF) mass spectrometer(MS) is used to map the protein content of ovarian surfaceepithelial cells (OSE) and an ovarian carcinoma-derivedcell line (ES2). The two dimensions involve the use ofliquid isoelectric focusing as the first phase and nonporous silica reversed-phase HPLC as the second phase ofseparation. Accurate molecular weight (MW) values arethen obtained upon the basis of ESI-TOFMS so that animage of isolectric point (pI) versus MW analogous to 2-Dgel electrophoresis is produced. The accurate MW together with the pI fraction and corresponding hydrophobicity (%B) are used to tag each protein so that proteinexpression can be compared in interlysate studies. Eachprotein is also identified on the basis of matrix-assistedlaser desorption−ionization (MALDI) TOFMS peptidemapping and intact MW so that a standard map isproduced against which other cell lines can be compared.Quantitative changes in protein expression are measuredin these interlysate comparisons using internal standardsin the on-line ESI-TOFMS process. In the ovarian epithelial cell lines under study, it is shown that in the three pIfractions chosen for detailed analysis, over 50 uniqueproteins can be detected per fraction, of which 40% canbe identified from web-based databases. It is also shownthat when using an accurate MW to compare proteins inthe OSE versus ovarian cancer sample, there are proteinshighly expressed in cancer cells but not in normal cells.In addition, many of the proteins in the cancer sampleappear to be down-regulated, as compared to the normalcells. This two-dimensional (2-D) liquid/mass mappingmethod may provide a means of studying proteins ininterlysate comparisons not readily available by othermethods.
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