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Cytochrome P-450 (P-450) enzymes catalyze the oxidation of a wide variety of substrates. Although a large number of P-450s have been characterized in different species and tissues, the mechanisms of catalysis of oxygenation may be understood in terms of a few basic principles. The chemistry is dominated by the ability of a high-valent formal (FeO)3+ species to carry out one-electron oxidations through the abstraction of hydrogen atoms, abstraction of electrons in n or pi orbitals, or the addition to pi bonds. A series of radical recombination reactions then completes the oxidation process. The protein structures are postulated to provide the axial thiolate ligand to the heme, to control the juxtaposition of the substrate (and therefore the regio- and stereoselectivity of oxidation), to alter the effective oxidation potential of the (FeO)3+ complex, and possibly to participate in specific acid/base catalysis in the oxidation of some substrates.
The gas-liquid chromatographic retention times on 0.5% SP-525 for 48 bile acids and related compounds as their methyl ester acetate derivatives are given. Ion tables for electron impact spectra have been compiled that permit direct access to ion structures for any given ion mass. Chemical ionization yields highly simplified mass spectra with two or three ions predominating for each compound. When the relative retention times of bile acids as their methyl ester acetates are combined with selective ion monitoring techniques in chemical ionization mass spectrometry, the retention time and ion mass number form a coordinate system which can be a powerful tool in the characterization of bile acid mixtures.