P450 Enzymes

51 000, 50000 and 51 000 respectively differ from one another and from isozymes a-e, and this is confirmed by antibody studies. Isozymes f and g showed a low activity towards all the substrates tested; h N-demethylated benzphetamine and hydroxylated zoxazolamine and 17b-oestradiol [D39]. These naming systems are also redundant.

Liver microsomes from phenobarbital-treated mice yield 4 P450 fractions with marginally different absorption spectra [A1699].

A monkey liver P450, molecular weight 50 000, catalyzes oxidations on a series of substrates, in the presence of a hydrogen transport system [D510].

Guinea pig isozymes, designated as the IIB family, molecular weight 52 000, hydroxylate D9-tetrahydrocannabinol and aniline, and demethylate p -nitroanisole [F819].

A mathematical analysis based on potential energy profiles during the reaction, based on arene oxide ring opening, gave a close approximation to the extent that the NIH shift (the migration of a substituent to a position ortho to its original position at the hydroxylation site) was observed for para hydroxylation, in agreement with the hypothesis that there is a p -quinoid intermediate. The data also support the hypothesis that there may be a pathway involving initial formation of a tetrahedral intermediate in the absence of epoxide formation [E284].

A full assessment of P450 enzymes is found in David Lewis ''Guide to Cytochromes P450'', Taylor & Francis, London (2001).

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