Rabbit liver microsomes

The samples of l,6-T2-DBpD and l,6-T2-2,3,7,8-Cl4-DBpD are useful in metabolism and mode of action studies. For example, when incubated with rabbit liver microsomes, l,6-T.>-DBpD is extensively metabolized to polar product(s) but only when these preparations are fortified with reduced nicotinamide-adenine dinucleotide phosphate. Under the same conditions l,6-T2-2,3,7,8-Cl4-DBpD is completely resistant to metabolic attack. In some types of studies, a higher specific activity possibly is desirable i.e., >1 Ci/mmole), and this can be achieved, with the methodology already developed, by using larger amounts of tritium gas or working on a larger synthetic scale so that it is not necessary to add unlabeled materials to assist in crystallization steps where a certain minimum amount of compound is necessary. 

Oae and coworkers oxidized several diaryl, dialkyl and alkyl aryl sulfides to their corresponding sulfoxides using purified cytochrome P-450 obtained from rabbit liver microsomes . In agreement with expectations, this enzyme did not exhibit much stereospecificity. Some examples including the observed e.e. values are shown by 121-125. A model was proposed to account for the absolute configurations of the sulfoxides produced (126). The sulfur atom is preferentially oxidized from the direction indicated. 

Sodium/glucose cotransporter (rabbit intestinal brush borders)1641 Stearylcoenzyme A desaturase (rat liver microsomal)[651 Subtilopeptidase amylosacchariticus[661 Succinate dehydrogenase (mitochondrial)1671... 

Seven carboxylesterase isoenzymes were purified from liver microsomes of mouse, hamster, guinea pig, rabbit, and monkey, and found to be glycoproteins hydrolyzing long-chain monoglycerides. Marked physical, enzymatic, and immunological similarities were found among these carboxylesterases, except for the monkey isoenzyme MK2 [99]. 

Dihydro-1,2-dihydroxybenzene (10.13) is oxidized by dihydrodiol dehydrogenase (EC 1.3.1.20) to catechol (10.15) (Chapt. 4 in [la]) [76], In a typical experiment in which 10.13 is incubated with phenobarbital-induced rabbit liver microsomes, phenol (10.14), catechol (10.15), and hydroquinone (10.16) represent 54, 39, and 1%, respectively, of the total metabolites detected [75]. In other words, neither benzene oxide (10.1) nor its hydration product l,2-dihydro-l,2-dihydroxybenzene (10.13) was detected. 

Cyclohexene oxide (1,2-epoxycyclohexane, 10.5, Fig. 10.29) has received particular attention as a substrate for EH (see Table 10.1). The compound has a meso-cis geometry like d.v-stilbcnc oxide (10.7), and, like the latter, is hydrated preferentially to the chiral (/ ,/ )-/ran.y-cyclohexane-1,2-diol (10.124) [185], There was a difference, however, between the activities of the rabbit liver microsomal and cytosolic EHs. The former was ca. 20-fold more active than the latter toward this substrate also, it formed the (R,R)-diol with 94% enantiomeric excess (ee) compared to only 22% ee for the cytosolic EH. 

Resistance to hydration was elucidated with tricyclic model compounds that lack the side chain and, hence, pharmacological activity. In this context, a useful comparison has been made between two meso compounds, namely 5W-dibenz.oja, dIcycloheplene 10,11-oxide (10.130, X = CH2) and d.v-slilbcnc oxide (10.7) [195]. The former compound proved to be a very poor substrate for rabbit liver microsomal EH, with a Km value comparable to that of cis-stilbene oxide, but Emax ca. 100-fold lower. This indicates that the two compounds have a comparable affinity for the enzyme, but that nucleophilic attack in the catalytic step is much less efficient for dibcnzo[ // cycloheplcnc 10,11-oxide than for d.v-slilbcnc oxide. This implies that the former compound acts better as an inhibitor than as a substrate of microsomal EH. Furthermore, there was also a fundamental steric difference in the reaction course of the two substrates, since the predominant stereoisomer formed from dibenzo //]cyclohep(ene 10,11-oxide had the (I OS, 11. -configuration,... 

Interestingly, there is a marked species difference in the in vitro hydrolysis of carbamazepine 10,11-epoxide, such that the reaction was observed only in liver microsomes from humans but not in liver microsomal or cytosolic preparations from dogs, rabbits, hamsters, rats, or mice [181][196], Thus, carbamazepine appears to be a very poor substrate for EH, in analogy with the simpler analogues 10.129 (X = RN, RCH, or RCH=C). The human enzyme is exceptional in this respect, but not, however, in the steric course of the reaction. The diol formed (10.131, X = H2NCON) is mostly the trans-(10.S, 11. S )-enaniiomer [196], In other words, the product enantioselectivity of the hydration of carbamazepine epoxide catalyzed by human EH is the same as that of di benzol a,oxide catalyzed by rabbit microsomal EH, discussed above. 

G. Bellucci, C. Chiappe, A. Cordoni, F. Marioni, The Rabbit Liver Microsomal Biotransformation of 1,1-Dialkylethylenes Enantioface Selection of Epoxidation and Enantioselectivity of Epoxide Hydrolysis , Chirality 1994, 6, 207 - 212. 

T. Watabe, K. Akamatsu, Oxidative Cleavage of the Ethylenic Linkage of Stilbene by Rabbit Liver Microsomes , Biochem. Pharmacol. 1975, 24, 442 - 444. 

Northern blot shows only hepatic expression in rabbit (Eggertsen et al., 1996). Found in rabbit liver microsomal fraction (Andersson et al., 1998). 

Collins, D. C., Williamson, D. G., and Layne, D. S., Enzymatic synthesis by a partially purified transferase from rabbit liver microsomes. J. Biol. Chem. 245, 873-876 (1970). 

LI. Labow, R. S., and Layne, D. S., The formation of glucosides of isoflavones and of some other phenols by rabbit liver microsomal fractions. Biochem. J. 128, 491-497 (1972). 

Heinemann, F. S. and Ozols, J. (1983) The complete amino acid sequence of rabbit phenobarbital-induced liver microsomal cytochrome P-450. J. Biol. Chem. 258, 4195-4201. 

ENRICHMENT IN PARAOXON FOLLOWING INCUBATION OF PARATHION WITH RABBIT LIVER MICROSOMES ... 

The studies described above have been carried out using hepatic microsomes from various mammalian species and purified cytochrome P-450-containing monooxygenases obtained from the livers of rabbits and rats. Additional studies have indicated the microsomes from rabbit ( ) and rat lung brain 21) also metabolize parathion in a manner similar to mammalian liver. 

The -oxygenation of cyanatryn occurred readily with liver microsomes and 10,000 g supernatant (the latter was fortified with GSH and the observed product was the glutathione conjugate [5]). The reaction could be detected in 2% liver homogenates but not in homogenates of kidney, lung, intestine, or caecal content. The reaction was readily catalyzed by microsomes from the livers of male and female rats, male and female rabbits and a male human (Table 1)(9). The rat sex difference was much larger for N-de-ethylation than for -oxidation. Typically, microsomes from male rats were more active than those from females. 

Investigation of the in vitro metabolism of delavirdine is accomplished using mouse, rat, dog, monkey, rabbit, and human liver microsomes. The primary metabolite observed is the A-dealkylated delavirdine 26. Another primary metabohte observed is the hydroxy-lation of the pyridine ring at C-6 (compound 27). The primary metabolism is by CYP3A4 and also CYP2D6. Delavirdine reduces the activity of CYP3A4, thereby inhibiting its own metabolism. 

Acute pyridine treatment (single intraperitoneal dose of 200 mg/kg bw) increased the metabolism of 2-butanol twofold in Sprague-Dawley rat liver microsomes and threefold in rabbit (New Zealand White) liver microsomes (Page Carlson, 1993). In liver microsomes from pyridine-treated (one intraperitoneal injection of 100 mg/kg bw, daily for four days) male Sprague-Dawley rats, increased oxidative biotransformation of the chlorofluorocarbon l,2-dichloro-l,l,2-trifluoroethane was found the day after the last injection (Dekant et al, 1995). 

Kaul, K.L. Novak, R.F. (1987) Inhibition and induction of rabbit liver microsomal cytochrome P-450 by pyridine. J. Pharmacol, exp. Ther., 243, 384-390 Kerckaert, G.A., Brauninger, R., LeBoeuf, R.A. Isfort, R.J. (1996) Use of the Syrian hamster cell transformation assay for carcinogenicity prediction of chemicals currently being tested by the National Toxicology Program in rodent bioassays. Environ. Health Perspect, 104 (Suppl. 5), 1075-1084... 

Johansson, I. Ingelman-Sundberg, M. (1985) Carbon tetrachloride-induced lipid peroxidation dependent on an ethanol-inducible form of rabbit liver microsomal cytochrome P-450. FEBS Lett., 183, 265-269... 

Urinary metabolites are S-methylthioacetic acid sulfoxide, V-acetyl-.S -methyl-L-cysteine and /-(methylthioacetyl)glycine, which are metabolites of Y-methyl-i-cysteine and 5-methylglutathione. These last two compounds were found after incubation of methyl chloride with rodent liver, kidney and brain homogenates. The methyl group of methyl chloride is metabolized via -methyl-L-cysteine to formate which is found in urine and blood of rats, whereas formaldehyde is found in rat liver microsomes and blood of mice and rabbits (lARC, 1986). 

Pentachloroethane is dechlorinated in the presence of a rabbit liver reconstituted cytochrome P450 system or by rat liver microsomes, NADPH and oxygen (without oxygen, it is metabolized to 96% trichloroethylene and 4% 1,1,2,2-tetrachloroethane) (lARC, 1986). 

Percutaneous absorption of phenyl glycidyl ether is high in rats and rabbits. It binds to glutathione in the presence of liver microsomes from various avian species (lARC, 1989). 

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