Initial purification and characterization of hepatic microsomal cytochrome P-450 from BNF-treated perch (Perca fluviatilis)

Tissue specificity of aryl hydrocarbon receptor (AhR) mediated responses and relative sensitivity of white sturgeon (Acipenser transmontanus) to an AhR agonist

Sturgeons are endangered in some parts of the world. Due to their benthic nature and longevity sturgeon are at greater risk of exposure to bioaccumulative contaminants such as dioxin-like compounds that are associated with sediments. Despite their endangered status, little research has been conducted to characterize the relative responsiveness of sturgeon to dioxin-like compounds. In an attempt to study the biological effects and possible associated risks of exposure to dioxin-like compounds in sturgeon, the molecular and biochemical responses of white sturgeon (Acipenser transmontanus) to a model aryl hydrocarbon receptor (AhR) agonist, β-naphthoflavone (βNF) were investigated. White sturgeon were injected intraperitoneally with one of three doses of βNF (0, 50, or 500mg/kg, bw). Rainbow trout (Oncorhynchus mykiss) were used as a reference species since their responses have been well characterized in the past. Three days following injection with βNF, fish were euthanized and livers, gills, and intestines collected for biochemical and molecular analyses. White sturgeon exposed to βNF had significantly greater ethoxyresorufin O-deethylase (EROD) activity in liver (up to 37-fold), gill (up to 41-fold), and intestine (up to 36-fold) than did unexposed controls. Rainbow trout injected with βNF exhibited EROD activity that was significantly greater in liver (88-fold), than that of controls, but was undetectable in gills or intestine. Abundance of CYP1A transcript displayed a comparable pattern of tissue-specific induction with intestine (up to 189-fold), gills (up to 53-fold), and liver (up to 21-fold). Methoxyresorufin O-deethylase (MROD) and pentoxyresorufin O-deethylase (PROD) activities were undetectable in unexposed white sturgeon tissues while exposed tissues displayed MROD activity that was only moderately greater than the activity that could be detected. Differential inducibility among liver, gill, and intestine following exposure to an AhR agonist is likely associated with tissue-specific regulation of the AhR signalling pathway. Liver and gill of white sturgeon had significantly greater AhR transcript abundance than did the intestine, however following exposure to βNF, significantly greater induction in AhR transcript abundance was detected in intestine (up to 35-fold) compared to liver (up to 5-fold) or gills (up to 11-fold). It was shown that white sturgeon are responsive to AhR agonists in the liver, gill, and intestine and could be among the more sensitive fish species with regard to inducibility of CYP1A.

Purification of CYP2B-like protein from feral leaping mullet (Liza saliens) liver microsomes and its biocatalytic, molecular, and immunological characterization

In this study, CYP2B-immunoreactive protein was purified to electrophoretic homogeneity from the liver microsomes of leaping mullet. The purified cytochrome P450 (CYP) gave a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis having a M(r) of 49,300 Da. Absolute absorption spectrum of the purified CYP showed a maximum at 417 nm and CO-difference spectrum of dithionite-reduced cytochrome P450 gave a peak at 450 nm. The purified CYP was found to be active in N-demethylation of benzphetamine, erythromycin, and ethylmorphine, and O-dealkylation of pentoxyresorufin in the reconstituted system. However, it was unable to catalyze O-dealkylation of ethoxyresorufin, methoxyresorufin, benzyloxyresorufin, and hydroxylation of lauric acid and aniline. The purified CYP showed strong cross-reactivity with anti-sheep lung CYP2B, a homologue of CYP2B4. N-terminal amino acid sequence of the mullet P450 had the highest degree of homology with CYP2Bs among the known CYPs. Spectral, electrophoretic, immunochemical, N-terminal amino acid sequence, and biocatalytic properties of the purified CYP are most similar to those of mammalian cytochrome P4502B. All these data indicate that the purified CYP is certainly 2B-like. In this study, we not only purified biocatalytically active CYP2B-like protein from fish, but also demonstrated detailed functional properties of CYP2B-like protein for the first time.

Cytochromes P-4501A, P-4503A and P-4502B in liver and heart of Mugil capito treated with CYP1A inducers

Hepatic microsomes of Aroclor 1254-treated Mugil capito showed a single protein band detected in immunoblot with monoclonal antibody 1-12-3 to teleost (scup) CYP1A. The hepatic CYP1A like protein was induced with dose dependency after exposure of the fish to β-naphthoflavone (BNF) as well as to Aroclor 1254. The induced mullet hepatic CYP1A protein was confined to a distinct fraction obtained by DE-52 anion exchange chromatography, and its relative content in that fraction increased in fish that were treated with higher doses of inducer. EROD (7-ethoxyresorufin O-deethylase) activity in hepatic microsomes from mullet treated with various doses of BNF correlated significantly (r(2)=0.81502, P<0.01) with CYP1A content. Treatment of the mullet with low dose of Aroclor 1254 (25 mg/kg) induced only traces of CYP1A in liver microsomes (5.1±4.8 mg/kg). However, in mullet treated with the high dose of Aroclor 1254 (100 mg/kg) there was a dramatic induction in CYP1A content (408±275 pmol/mg) and this hemoprotein comprised about 83% of the total P-450 content of liver microsomes. The total level of P-450, although induced in the liver tissue, was not induced in heart tissue of Aroclor 1254 treated mullet. On the other hand, P-4501A was induced in treated mullet to a level that comprised almost all of the cardiac P-450 content. EROD activity in the heart tissue of induced mullet was characterized by low V(max) and high K(m) values (K(m)=2.35 mM, V(max)=39.5 pmol/min per mg) compared to the values recorded for the enzyme from the liver (K(m)=1.0 mM, V(max)=288.0 pmol/min per mg). Cardiac CYP1A with low catalytic activity and repression of CYP-types other then CYP1A in heart of CYP1A induced fish may be part of a mechanism aimed to preserve crucial levels of electron donors and molecular oxygen in cardiac muscle of fish exposed to CYP1A inducers.