Characterization Of Microsomal Cytochrome P-450 Research Articles

Purification and characterization of microsomal cytochrome P-450 from spider crabs, Libinia sp.

Purification and characterization of microsomal cytochrome P-450 from spider crabs, Libinia sp.

Spectral characterization of microsomal cytochrome P-450 from the midgut of the tobacco hornworm, Manduca sexta J.

Absolute absorption spectra and the spectral interactions of 42 xenobiotics with the midgut microsomal cytochrome P-450 from the tobacco hornworm were studied. The study of type II optical difference spectra using several ligands revealed that the basic requirements for this perturbation are the same as in other animal species, namely, a sterically accessible sp 2 or sp 3 nitrogen atom. An unusual spectral interaction involving both cytochrome P-450 and cytochrome b 5 was observed with n- octylamine and certain other amines. The spectral data are discussed in relation to the current ideas on the spectral characterization of microsomal cytochrome P-450. Type I difference spectra were observed with pinacolone, Bux, malathion and an insecticide synergist sulfoxide. However, this spectral response was not observed with several ligands such as benzphetamine, SKF-525A and other compounds known to be type I with microsomes from other animal species.

Occurrence and characterization of microsomal cytochrome P-450 in several vertebrate and insect species

1. 1. Microsomal cytochrome P-450s from 19 species, including mammals, birds, fish and insects, were characterized by optical difference spectra formed by this interaction with a number of ligands. 2. 2. These include: carbon monoxide; benzphetamine (type I); pyridine (type II); n-octylamine (type II); ethyl isocyanide (type III). 3. 3. In addition the following enzyme activities were determined: O-demethylation of p-nitroanisole; NADPH oxidation; NADPH-cytochrome reductase (E.C. 1.6.2.3). 4. 4. Both quantitative and qualitative differences exist between the microsomal cytochrome P-450s of various animal species but differences in enzyme activity cannot be correlated with any single spectral characteristic.

Microsomal cytochrome P-450 from the housefly, Musca domestica: Assay and spectral characterization

The effects of assay conditions on spectral characterization of microsomal cytochrome P-450 from insecticide-resistant (Fc) and insecticide-susceptible (CSMA) strains of the housefly, ( Musca domestica) were investigated. The specific activity of cytochrome P-450 was higher in microsomes prepared from isolated abdomens than in those from whole flies. Buffers of low molarity (<0·1 M) caused denaturation of cytochrome P-450 and the optimum pH values, in terms of cytochrome P-450 content, were pH 7·0 and 7·2 for microsomes of Fc and CSMA houseflies respectively. Guidelines were established to reduce errors in measurement and interpretation of substrate difference spectra. Cytochrome P-420 did not exhibit normal type I and type II difference spectra, however, its presence in microsomes interfered with the evaluation of the type III difference spectra of ethyl isocyanide and pyridine. Some strain specific differences were noted in the oxidized difference spectra of type I and type II ligands and in those obtained with microsomes pretreated with either NADH or NADPH. Microsomes from neither strain exhibited normal type I difference spectra with benzphetamine in the presence of dithionite. The data obtained are discussed in relation to current methodology used with microsomal cytochrome P-450 from insects and other taxonomic groups.