Identification of human liver cytochromes P450 by using MALDI-TOF mass spectrometry

Proteomic approaches have been used for detection and identification of cytochromes P450 forms from highly purified membrane preparations of human liver. These included the protein separation by 2D-and/or 1D-electrophoresis and molecular scanning of a SDS-PAGE gel fragment in a range 45–66 kDa (this area corresponds molecular weights of cytochromes P450). The analysis of protein content was statistically evaluated by means of an original 1D-ZOOMER software package which allowed to carry out the processing of mass spectra mixture instead of individual mass spectra used by standard techniques. In the range 45–66 kDa we identified 13 microsomal membrane proteins including such cytochrome P450 forms as CYPs 1A2, 1B1, 2A6, 2E1, 2C8, 2C9, 2C10, 2D6, 3A4, 4A11, 4F2. Study of enzymatic activities of human liver microsomal cytochrome P450 isoforms CYP 1A, 2B, 3A, and 2E revealed the decrease in the rates of O-dealkylation and N-demethylation catalyzed by CYP 450 1A1/1A2 and 3A4 under pathological conditions, whereas 7-benzyloxyresorufin-O-debenzylase activity (which characterizes the total activity of CYP 2B and CYP 2C), the activities of CYP 2E1 (methanol oxidation), 7-pentoxyresorufin-O-dealkylation (CYP 2B), 7-ethoxy-and 7-methoxycoumarin-O-dealkylases (CYP 2B1) remained basically unchanged.