scholarly journals Dimethylnitrosamine demethylation by reconstituted liver microsomal cytochrome P-450 enzyme system

1975 ◽  
Vol 152 (3) ◽  
pp. 705-708 ◽  
Author(s):  
P D Lotlikar ◽  
W J Baldy ◽  
E N Dwyer
Keyword(s):  
Cytochrome C ◽  
Enzyme System ◽  
Microsomal Cytochrome ◽  
Cytochrome C Reductase ◽  
Oxidative Demethylation ◽  
Enzyme Systems ◽  
Triton X ◽  
Cytochrome P 450 ◽  
Nadph Cytochrome C Reductase ◽  
Demethylation Activity

Oxidative demethylation of dimethylnitosamine was studied with both reconstituted and unresolved liver microsomal cytochrome P-450 enzyme systems from rats and hamsters. Proteinase treatment of liver microsomal preparations yielded cytochrome P-450 particulate fractions. Both cytochrome P-450 and NADPH- cytochrome c reductase fractions were required for optimum demethylation activity. Particulate cytochrome P-450 fractions were more effecient than either Triton X-100- or cholatesolubilized preparations of these particles in demethylation activity with rat and hamster liver preparations appear to be due to differences in specificity in their cytochrome P-450 fractions.

scholarly journals Ring-and N-hydroxylation of 2-acetamidofluorene by rat liver reconstituted cytochrome P-450 enzyme system

1975 ◽  
Vol 150 (3) ◽  
pp. 561-564 ◽  
Author(s):  
P D Lotlikar ◽  
K Zaleski
Keyword(s):  
Cytochrome C ◽  
Rat Liver ◽  
Enzyme System ◽  
Partial Purification ◽  
Hydroxylated Metabolites ◽  
Triton X ◽  
Cytochrome P 450 ◽  
Ring Hydroxylation ◽  
Hydroxylation Activity ◽  
Nadph Cytochrome C Reductase

The N- and ring-hydroxylation of 2-acetamidofluorene were studied with a reconstituted cytochrome P-450 enzyme from microsomal fractions of liver from both control and 3-methylcholanthrene-pretreated rats. Proteinase treatment and Triton X-100 solubilization were two important steps for partial purification of the cytochrome P-450 fraction. Both cytochrome P-450 and NADPH-cytochrome c reductase fractions were required for optimum N- and ring-hydroxylation activity. Hydroxylation activity was determined by the source of cytochrome P-450 fraction; cytochrome P-450 fraction from pretreated animals was severalfold more active than the fraction from controls. Formation of N-hydroxylated metabolites with reconstituted systems from both control and pretreated animals was greater than that with their respective whole microsomal fractions.

Temperature Influence on Basal Activity and Induction of Mixed Function Oxygenase Activity in Fundulus heteroclitus

1979 ◽  
Vol 36 (11) ◽  
pp. 1400-1405 ◽  
Author(s):  
John J. Stegeman
Keyword(s):  
Cytochrome C ◽  
Fundulus Heteroclitus ◽  
Reductase Activity ◽  
Control Fish ◽  
Cytochrome C Reductase ◽  
Nadph Cytochrome ◽  
Pyrene Hydroxylase ◽  
Mixed Function Oxygenase ◽  
Cytochrome P 450 ◽  
Nadph Cytochrome C Reductase

Treatment of Fundulus heteroclitus acclimated to 6.5 °C with benzo(a)pyrene did not elicit any change in the levels of hepatic microsomal NADH- or NADPH-cytochrome c reductase activity, nor in the levels of cytochrome P-450 or its catalytic activities. However, the same treatment offish at 16 5 °C resulted in a marked induction of benzo(a)pyrene hydroxylase and NADPH-cytochrome c reductase. Cytochrome P-450 content was also higher in the warm, treated fish and the Soret maximum of reduced, CO-treated microsomes was shifted to the violet. Levels of aminopyrine demethylase and NADH-cytochrome c reductase activities did not show a significant treatment effect. At neither temperature could treated and control fish be distinguished on the basis of in vitro inhibition of benzo(a)pyrene hydroxylase activity by 7,8-benzoflavone. Levels of NADPH-cytochrome c reductase and benzo(a)pyrene hydroxylase activities were greater in control Fundulus acclimated to 6.5 °C than to 16.5 °C, when normalized to microsomal protein, but not when based on body weight. The results indicate that habitat temperature alone may not affect the capacity for initial hydrocarbon metabolism in fish, but that it can strongly influence the induction of cytochrome P-450. Key words: temperature, cytochrome P-450, hydrocarbon metabolism, mixed-function oxygenase, Fundulus heteroclitus

Release of ferrous iron from ferritin by liver microsomes: a possible role in the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin

1984 ◽  
Vol 62 (12) ◽  
pp. 1293-1300 ◽  
Author(s):  
Bruce Rowley ◽  
George D. Sweeney
Keyword(s):  
Cytochrome C ◽  
Flavin Mononucleotide ◽  
Monooxygenase System ◽  
Iron Release ◽  
Cytochrome C Reductase ◽  
Nadph Cytochrome ◽  
Ferritin Iron ◽  
Tetrachlorodibenzo P Dioxin ◽  
Cytochrome P 450 ◽  
Nadph Cytochrome C Reductase

Nonheme iron is synergistic with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in producing hepatotoxicity in mice. Fe2+ rather than Fe3+ is the probable toxin and we speculated that TCDD, an inducer of microsomal electron transport, might favour reduction of iron. We have defined a system which will release Fe2+ from ferritin (Fe3+) under anaerobic conditions and in the presence of added flavin mononucleotide (FMN). The rate of reduction of ferritin iron was proportional (a) to microsomal protein from 0.5 to >3 mg/mL, (b) to the activity of NADPH–cytochrome c reductase over 0.1 U/mL, (c) to ferritin at concentrations exceeding iron concentrations >200 μmol/L, and (d) to the concentration of FMN when it was less than 125 μmol/L. The system was approximately twice as active with NADPH as with NADH as electron donor. The linear phase of iron release did not commence immediately, but followed a delay (±0.5 min) after adding FMN to an anaerobic mixture containing microsomes, ferritin, an NADPH-generating system, and an oxygen-scavenging system. When microsomes from untreated, Phenobarbitaltreated (3 days), or TCDD-treated (1 or 3 weeks) rats were compared, iron release correlated most closely with the cytochrome P-450 concentration. However, when the microsomal proteins were solubilized and the NADPH–cytochrome c reductase and cytochrome P-450 activities were separated, reduction of ferritin iron was shown to be a function only of the reductase fraction, except that the delay in initiating release of Fe2+ was increased with purified reductase and decreased when a monooxygenase system was reconstituted with cytochrome (phenobarbital or TCDD induced) and lipid. These studies have defined a potentially important hepatic microsomal system able to release Fe2+ from ferritin iron, but have failed to indicate any feature unique to the dioxin-induced monooxygenase system.

Sign in / Sign up

Export Citation Format

Share Document