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E T Morgan

Publications and source records attributed to E T Morgan.

At least 55 records · Page 3Linked to original sources
PubMed1991

Growth hormone-dependent and -independent regulation of cytochrome P-450 isozyme expression in streptozotocin-diabetic rats.

The sexually dimorphic GH secretory pattern is thought to be the major factor regulating constitutive expression of hepatic P450IIC11 (P-450h) and P450IIC12 (P-450i). In this study we investigated whether factors other than the diabetes-induced decrease in GH secretion contribute to alterations in P-450 isozyme expression in streptozotocin (STZ)-diabetic rats. In male rats, hepatic P-450h apoprotein and mRNA decreased to 13% and 24% of control male levels, respectively, within 14 days of STZ injection. STZ-diabetes had little effect on expression of P-450i in females. Treatment of diabetic male rats with GH did not reverse the suppression of P-450h. STZ treatment also suppressed P-450h expression in GH-treated hypophysectomized (Hx) male rats, but incompletely. Thus, GH can partially reverse diabetic suppression of P-450h. However, in Hx male rats without GH supplementation, STZ treatment suppressed P-450h apoprotein and mRNA expression to 16% and 6% of nondiabetic Hx male levels, respectively, demonstrating the existence of GH-independent regulation of P-450h expression. In Hx female rats, P-450h apoprotein levels were 40% of those in intact control males and were not significantly decreased by STZ. Concomitantly, STZ produced a greater decrease in serum insulin levels and a greater increase in serum glucagon in Hx male rats than in Hx females. The results provide evidence for the existence of STZ-sensitive GH-independent expression of P-450h and further document the gender differences in STZ sensitivity.

Alpha-Globulins↗
PubMed1991

Regulation of cytochrome P450IIC12 expression by interleukin-1 alpha, interleukin-6, and dexamethasone.

During the acute phase response to bacterial endotoxin in rats, hepatic levels of cytochrome P450IIC12 [AH, reduced flavoprotein:oxygen oxidoreductase (RH hydroxylating), EC 1.14.14.1] (P450IIC12) apoenzyme and mRNA are suppressed. We set out to determine the effects of potential humoral mediators of inflammation on the expression of P450IIC12 in female rats. A single injection of 12,000 or 60,000 units of interleukin-1 alpha had no effect on total cytochrome P450 content or P450IIC12 mRNA measured 12 hr later, although P450IIC12 apoenzyme was slightly but significantly increased by the higher dose. In the second experiment, animals were given dexamethasone (100 micrograms/kg at -30 min), interleukin-1 alpha (30,000 units/kg at 0, 2, and 4 hr), or both and were sacrificed at 12 hr. Treatment with interleukin-1 alpha alone significantly suppressed total cytochrome P450, P450IIC12 apoenzyme, and P450IIC12 mRNA to 77, 53, and 65% of control levels, respectively; beta-actin mRNA was significantly increased (206% of control levels). Treatment with dexamethasone alone suppressed total cytochrome P450 and P450IIC12 mRNA (73% of controls) but did not significantly affect P450IIC12 apoenzyme measured 12.5 hr later. Again, beta-actin mRNA was increased. When both interleukin-1 alpha and dexamethasone were given, total cytochrome P450 and P450IIC12 mRNA (43% of controls) were suppressed, and beta-actin mRNA was significantly increased. In the third experiment, animals were injected at 0 and 12 hr with dexamethasone (83 micrograms/kg), interleukin-6 (33 micrograms/kg), or both. Interleukin-6 alone did not significantly affect total cytochrome P450 or P450IIC12 apoenzyme or mRNA. Dexamethasone alone suppressed P450IIC12 apoenzyme and mRNA (to 52 and 41%, respectively, of controls). Treatment with both interleukin-6 and dexamethasone significantly suppressed total cytochrome P450 and P450IIC12 apoenzyme and mRNA; suppression of P450IIC12 mRNA (to 16% of controls) was greater than with dexamethasone alone. No change in the transcription rate of CYP2C12 was observed 24 hr after initiation of treatment with dexamethasone (83 micrograms/kg at 0 and 12 hr) or 12 hr after initiation of treatment with interleukin-1 alpha (30,000 units/kg at 0, 2, and 4 hr). We conclude that, in this model, interleukin-1 alpha and glucocorticoids are important mediators of the suppression of hepatic P450IIC12 expression during inflammation. Interleukin-6 was not as potent, but it did potentiate the effects of dexamethasone. Suppression of P450IIC12 expression by dexamethasone and interleukin-1 alpha appeared to be mediated at a pretranslational level, but the possibility of a transcriptional effect needs to be further investigated.

Actins↗
PubMed1990

Transcriptional and post-transcriptional suppression of P450IIC11 and P450IIC12 by inflammation.

Induction of inflammation in rats by treatment with endotoxin or turpentine is known to suppress levels of hepatic mRNAs for P450IIC11 and P450IIC12. We report that transcription of CYP2C12 in female rats is not significantly reduced from control levels; suppression of this gene during inflammation appears to be mediated post-transcriptionally. In contrast, transcription of CYP2C11 in male rats is reduced to 23% and to 5% of control levels by turpentine and by endotoxin, respectively. Sex-specificity of CYP2C11 expression is also regulated transcriptionally, whereas sex-specificity of CYP2C12 expression appears to be regulated by a post-transcriptional mechanism.

Animals↗
PubMed1989

Suppression of constitutive cytochrome P-450 gene expression in livers of rats undergoing an acute phase response to endotoxin.

Administration of purified bacterial lipopolysaccharide (LPS) to male rats suppressed the constitutive hepatic expression of the male-specific cytochrome P-450 [AH, reduced flavoprotein:oxygen oxidoreductase (RH hydroxylating), E.C.1.14.14.1] isozyme P-450h (P450IIC11) to about 35% of control levels within 24 hr. The mRNA for P-450h was more rapidly and more profoundly suppressed than was the protein, indicating (a) that the decrease in the mRNA was responsible for the suppression of the protein and (b) that other mechanisms work to maintain expression of P-450h apoprotein in the face of repression of its mRNA. Suppression of P-450h expression was maximal at an endotoxin dose of 30-100 micrograms/kg, indicating that P-450 suppression is concomitant with the acute-phase response of hepatic secretory proteins. The female-specific cytochrome P-450 isozyme, P-450i (P450IIC12), was suppressed to 17% of control levels by LPS administration in female rats. Suppression of the P-450i apoprotein by LPS, and recovery of its expression, was more rapid than was suppression of P-450h in males. P-450i protein and mRNA levels were concomitantly suppressed by LPS, indicating that although there is a pretranslational component to the suppression, other mechanisms may also contribute. Calculations based on estimations of the microsomal contents of P-450h and P-450i relative to the total cytochrome P-450 in untreated rat livers indicate that suppression of these forms contributes significantly to the decreases in total microsomal P-450 after LPS treatment. In these studies, hepatic microsomal NADPH-cytochrome c reductase (TPNH2-cytochrome c reductase, E.C.1.6.2.4) activities and content of cytochrome b5 were decreased by LPS administration in both male and female rats. Like its effects on cytochrome P-450 expression, endotoxin suppression of NADPH-cytochrome c reductase activities and cytochrome b5 levels was more rapid in female rats than in males. The production of a local inflammatory response in male rats by subcutaneous injection of turpentine caused effects on cytochrome P-450, P-450h expression, and cytochrome b5 that were similar to those of endotoxin but were less rapidly achieved.

Acute-Phase Reaction↗
PubMed1987

A dioestrous increase in thymocyte proliferation during the oestrous cycle.

Coitus, which precedes internal fertilisation, is a unique physiological event which allows motile allogeneic spermatozoa to enter the female host and invade her tissues. The cyclic cellular proliferation observed in the thymus of the female rat may be an important preparation of her immune system for this event.

Animals↗
PubMed1987

Preparation and characterization of monoclonal antibodies recognizing unique epitopes on sexually differentiated rat liver cytochrome P-450 isozymes.

Cytochrome P-450 isozymes P-450(16 alpha), P-450(15 beta), and P-450DEa are immunochemically related, as indicated by mutual cross-reactivity with polyclonal antibody preparations. We have isolated five monoclonal antibodies to P-450(15 beta) and one antibody to P-450(16 alpha) that show selectivity for the respective antigens. High frequencies of cross-reactivity were observed, indicating a high degree of homology among P-450(16 alpha), P-450(15 beta), and P-450DEa. All of the P-450(15 beta-specific antibodies bound to the same epitope, or closely grouped epitopes, supporting this conclusion. The specificity of each monoclonal antibody was characterized by enzyme-linked immunosorbent assay. Western immunoblotting, and antibody-Sepharose immunoadsorption of solubilized rat liver microsomes. Antibodies F22 and F23, which were apparently identical, were specific for P-450(15 beta) by these criteria. However, the apparent specificities of antibodies F3 and F20 for P-450(15 beta), and of M16 for P-450(16 alpha), were highly dependent on the analytical technique used. The five anti-P-450(15 beta) antibodies all inhibited the catalytic activity of microsomal P-450(15 beta), by a maximum of 70%. However, they also produced a similar inhibition of microsomal P-450(16 alpha-specific antibody M16 and F23 have a low-affinity interaction with an epitope on P-450(16 alpha). The P-450(16 alpha)-specific antibody M16 was not inhibitory. The results indicate that the apparent specificity of a monoclonal antibody for an antigen determined by, e.g., Western blotting does not allow the conclusive identification of a protein in another system, e.g., immunoprecipitation of in vitro translation reaction products.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Growth hormone regulates expression of rat liver cytochrome P-450 15 beta at a pretranslational level.

Polyclonal antibodies to rat liver microsomal cytochrome P-450 15 beta-hydroxylase were used to screen a female rat liver cDNA expression library. Recombinant plasmid C-6, isolated from a positive colony, contained a cDNA of 1000 base pairs which hybridized to a single, 1.7 kilobase class of mRNA on Northern blot analysis. Semi-quantitative slot blots showed that the level of this mRNA was 17-fold lower in male rat liver than in females. Continuous infusion of human growth hormone to male rats caused them to express female levels of C-6 mRNA, while the same daily dose of hormone given intermittently had no effect. A high degree of correlation of the levels of C-6 mRNA with 15 beta-hydroxylase protein levels and catalytic activities was found, demonstrating that the sexually differentiated, growth hormone-dependent expression of the 15 beta-hydroxylase is regulated at a step preceding translation.

Animals↗
PubMed1986

Oxidation of tricyclic antidepressant drugs, debrisoquine and 7-ethoxyresorufin, by human liver preparations.

Data obtained from human studies in vivo show that the dispositions of the tricyclic antidepressant drugs desmethylimipramine (DMI) and nortriptyline are related to the debrisoquine hydroxylation phenotype. To obtain insight into the enzymic mechanisms behind this, the metabolism of debrisoquine and antidepressant drugs by human liver preparations have been studied. The 2-hydroxylation of DMI in vitro correlates with the 4-hydroxylation of debrisoquine among various livers (rs = 0.90). Debrisoquine inhibits DMI hydroxylation competitively, and DMI inhibits debrisoquine hydroxylation, suggesting that DMI hydroxylation is catalysed by the debrisoquine hydroxylase in human liver. By monitoring the hydroxylation of DMI in various fractions during separation and purification of cytochrome P-450 from human liver microsomes we have purified a cytochrome P-450 which efficiently hydroxylates this drug. The apparently electrophoretically homogeneous enzyme had a molecular weight of 51,500 and hydroxylated DMI and debrisoquine at rates of up to 0.95 and 0.45 nmol/min . nmol P-450, respectively. This is probably the major debrisoquine hydroxylating cytochrome P-450 in man. Nortriptyline 10-hydroxylation correlates strongly (r = 0.96) with debrisoquine hydroxylation in human liver microsomes. Nortriptyline inhibits DMI-hydroxylation competitively, and the drug also inhibits the 4-hydroxylation of debrisoquine. Thus it is probable that nortriptyline is hydroxylated by debrisoquine hydroxylase. Imipramine N-demethylation did not correlate significantly (P greater than 0.1) with debrisoquine hydroxylation among microsomes from nine livers. However, if a liver from a subject, which was a poor metabolizer of debrisoquine in vivo, was included, a correlation was obtained (r = 0.79, P less than 0.01, N = 10). Imipramine demethylation also correlated with DMI-hydroxylation only if the 'poor metabolizer' liver was included (r = 0.75, P less than 0.05, N = 10). Debrisoquine inhibited imipramine demethylation competitively. The data indicate that imipramine can interact with debrisoquine- and DMI-hydroxylase, but it is uncertain if this enzyme plays an important quantitative role in its demethylation. Ethoxyresorufin O-deethylation correlated with DMI hydroxylation (r = 0.80) in human liver preparations, and DMI inhibited the former reaction in what is probably a mixed competitive-non-competitive inhibition. Liver preparations from a subject who was a poor oxidizer of debrisoquine both in vivo and in vitro had unusually low capacity to metabolize ethoxyresorufin. Thus ethoxyresorufin, at least partly, seems to interact with an enzyme that can metabolize DMI in human liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1985

Hormonal and developmental regulation of expression of the hepatic microsomal steroid 16 alpha-hydroxylase cytochrome P-450 apoprotein in the rat.

The hormonal regulation of the sexually differentiated cytochrome P-450 isozyme which catalyzes 16 alpha-hydroxylation of testosterone and 4-androstene-3,17-dione in male rat liver (P-450(16) alpha) was investigated. Estradiol valerate injection of male rats caused a decrease in P-450(16) alpha levels to almost the female level, while methyltrienolone injection had the reverse effect in female animals. Hypophysectomy abolished the sex difference in P-450(16) alpha levels. Human growth hormone infusion into male rats, mimicking the female pattern of growth hormone secretion, caused a feminization of P-450(16) alpha levels. The same effect was also seen in hypophysectomized rats of both sexes. In contrast, a different administration schedule involving 12 h injections of human growth hormone, mimicking the male pattern of growth hormone secretion, caused a masculinization of P-450(16) alpha levels in hypophysectomized rats, at a daily dose which causes feminization when given by infusion. Thus, the level of expression of P-450(16) alpha in the liver is dependent on the temporal pattern of blood growth hormone levels. While infusion of rat growth hormone into male rats also feminized the P-450(16) alpha levels, infusion of ovine prolactin had no effect. Ontogenic studies showed that the developmental pattern of P-450(16) alpha expression in the liver coincided with the known pattern of development of the sexual differentiation of hepatic steroid 16 alpha-hydroxylase activity and of the diurnal pattern of growth hormone secretion.

Aging↗
PubMed1985

Hypothalamo-pituitary regulation of cytochrome P-450(15) beta apoprotein levels in rat liver.

The regulation of the sexually differentiated steroid sulfate 15 beta-hydroxylase, cytochrome P-450(15) beta of female rat liver has been investigated. Specific antibodies raised to isozyme P-450(15) beta were used with the Western blot technique to quantitate the specific levels of P-450(15) beta in liver microsomes. The method demonstrated that the levels of the protein are about 16-fold higher in female than in male microsomes and also showed that the specific microsomal content of P-450(15) beta is controlled by GH. Hypophysectomy of female animals resulted in a decrease of P-450(15) beta to male levels. Continuous infusion of human GH, mimicking the female pattern of GH secretion in intact male animals, caused an elevation of the P-450(15) beta level to that of the female. The same dose of human GH in hypophysectomized male or female animals raised the P-450(15) beta level 8-fold or 50% of that seen in normal females. Infusion of ovine PRL to intact male rats had no effect on P-450(15) beta levels, whereas infusion of rat GH caused a 4-fold increase. Thus, the regulation of P-450(15) beta by GH is mainly associated with the somatogenic properties of the hormone. Furthermore, sc injection of rat GH every 12 h, mimicking the male pattern of GH secretion, had no effect on P-450(15) beta levels, demonstrating the importance of the GH secretory pattern in regulation of the specific protein levels. Postpubertal castration of male animals did not influence the microsomal P-450(15) beta content, whereas neonatal castration led to a feminization of the P-450(15) beta content in the adult male rat. Administration of estradiol valerate to male animals caused complete feminization of P-450(15) beta levels, whereas administration of androgen to female animals caused a decrease to male levels. Before 21 days of age, the P-450(15) beta level was slightly higher in male than in female rats. At 35 days, however, the P-450(15) beta level in female rats had increased almost 100-fold, whereas the levels in males increased only slightly. These changes are concomitant with the development of the sexual differentiation of the GH secretory pattern, supporting the role of GH in P-450(15) beta regulation. In conclusion, isozyme P-450(15) beta is a GH-regulated enzyme specific for female rats. The low level of the protein in males is probably explained by neonatal androgenic programming of the GH secretory pattern.

Androgens↗
PubMed1985

Sexual differentiation of cytochrome P-450 in rat liver. Evidence for a constitutive isozyme as the male-specific 16 alpha-hydroxylase.

Cytochrome P-450 isozyme RLM5 [Cheng, K-C., and J.B. Schenkman, J. Biol. Chem. 257:2378-2385 (1982)], possessing a high steroid 16 alpha-hydroxylating activity, was isolated from male rat livers, and the hypothesis that this protein is the sexually differentiated 16 alpha-hydroxylase was tested. Isozyme RLM5 was not detected when the same purification procedure was applied to female rat liver microsomes. However, a female isozyme named DEa and possessing a similar Mr was obtained from similar column fractions. The DEa isozyme had insignificant steroid-hydroxylating activity and a substrate specificity different from isozyme RLM5. The two proteins could also be distinguished in their primary structures and immunochemical properties. Rabbit antibodies were raised to isozyme RLM5 and were made specific by immunoabsorption with a crude female cytochrome P-450 fraction coupled to Affi-Gel 10. The antibodies were used in a Western blot immunoassay to demonstrate that isozyme RLM5 can be detected in liver microsomes of male rats at levels at least 20 times higher than those in the female, and that its sexual differentiation is neonatally imprinted by androgen. The antibodies were able to specifically inhibit 70% of the testosterone 16 alpha-hydroxylase activity in male rat liver microsomes but had no effect on the activity in females. It was concluded that isozyme RLM5 is the major sexually differentiated microsomal 16 alpha-hydroxylase.

Animals↗
PubMed1985

Isozyme selectivity of the inhibition of rat liver cytochromes P-450 by chloramphenicol in vivo.

The isozyme-selectivity of chloramphenicol as an inhibitor of rat liver cytochromes P-450 has been investigated. Untreated rats and rats treated with the inducers phenobarbital, beta-naphthoflavone, pregnenolone 16 alpha-carbonitrile, and clofibrate have been injected intraperitoneally with chloramphenicol, and inhibition of specific cytochrome P-450 isozymes has been assessed by monitoring the metabolism of warfarin, testosterone, isosafrole, or lauric acid in subsequently prepared hepatic microsomal preparations. Of eight major cytochrome P-450 isozymes which could be monitored in this fashion, three were inhibited by more than 50% by a dose of chloramphenicol of 300 mg/kg, whereas no evidence of inhibition of the remaining isozymes was obtained. P-450PB-C, an isozyme which is present in significant amounts in untreated rats and which is induced approximately 2-fold by phenobarbital, was the most susceptible cytochrome P-450 to inhibition by chloramphenicol both in vivo and in vitro. P-450PB-B, the major phenobarbital-inducible isozyme, and P-450UT-A, a male-specific testosterone 2 alpha- and 16 alpha-hydroxylase, were intermediate in their susceptibility to chloramphenicol. In contrast, the major isozymes induced by beta-naphthoflavone, pregnenolone 16 alpha-carbonitrile, and clofibrate, as well as a constitutive testosterone 7 alpha-hydroxylase, were not inhibited by chloramphenicol.

Animals↗
PubMed1984

Purification, characterization, and pituitary regulation of the sex-specific cytochrome P-450 15 beta-hydroxylase from liver microsomes of untreated female rats.

A sex-differentiated form of cytochrome P-450 has been purified to electrophoretic homogeneity from liver microsomes of untreated female rats. The purified preparation contained 17 nmol of P-450/mg of protein and had a minimum molecular weight of 50,000. The final preparation was active in the hydroxylation of 5 alpha-[3H]androstane-3 alpha, 17 beta-diol 3,17-disulfate in the 15 beta position, with a turnover number of 2.6 nmol/min/nmol P-450 and is designated "P-450 15 beta" on the basis of this activity. Cytochrome P-450 15 beta is isolated essentially in the low-spin state and has a CO-reduced difference spectral maximum at 449 nm. Comparison of the female protein with the corresponding P-450 fraction from male rats revealed an absence of the 15 beta band in the male electrophoretic profile. Specific antibodies to isozyme 15 beta were used with a Western blot technique to demonstrate the virtual absence of the protein in male microsomes. This method was also used to demonstrate that hypophysectomy of female rats resulted in undetectable levels of the 15 beta-hydroxylase, while continuous infusion of growth hormone to normal male animals increased the 15 beta-hydroxylase level to that of female. P-450 15 beta is proposed to be the enzyme responsible for the predominance of 15 beta-hydroxylated steroid sulfate metabolites in excreta of female rats, and their absence in males. The same purification procedure for female rat liver microsomes also yielded another purified cytochrome P-450 characterized by a minimum molecular weight of 52,500, termed P-450 DEa, which was inefficient in the 15 beta-hydroxylation of 5 alpha-[3H]androstane-3 alpha, 17 beta-diol 3, 17-disulfate. No evidence was obtained that this form is sexually differentiated.

Animals↗
PubMed1983

Comparison of six rabbit liver cytochrome P-450 isozymes in formation of a reactive metabolite of acetaminophen.

This laboratory has recently reported the isolation of an ethanol-inducible form of rabbit liver microsomal cytochrome P-450, designated isozyme 3a. In view of the reports of others that the hepatotoxicity of acetaminophen is increased in ethanol-treated animals and the human alcoholic, we have determined the activity of the six available P-450 isozymes in the activation of the drug to give an intermediate which forms a conjugate with reduced glutathione. Isozymes 3a, 4, and 6, all of which are present in significant amounts in the liver microsomes from rabbits chronically administered ethanol, exhibited the highest activities in the reconstituted enzyme system, whereas isozymes 3b and 3c were 10- to 20-fold less effective, and phenobarbital-inducible isozyme 2 was essentially inactive, even in the presence of cytochrome b5. The results obtained thus indicate that induction by ethanol of P-450 isozyme 3a (or a homologous enzyme in other species) may contribute to the toxicity of acetaminophen but that other cytochromes also play a significant role.

Acetaminophen↗
PubMed1983

Alcohol oxidation by isozyme 3a of liver microsomal cytochrome P-450.

Liver microsomes from rabbits treated chronically with ethanol were solubilized and fractionated to yield a new isozyme of cytochrome P-450 in a homogeneous state. This cytochrome, designated as isozyme 3a on the basis of its relative electrophoretic mobility, is distinct from the known terminal amino acid sequences. In addition, peptide mapping by high performance liquid chromatography following trypsinolysis indicates that form 3a is a unique gene product. This cytochrome has unusually high activity in the oxidation of ethanol and other alcohols to aldehydes and in the rho-hydroxylation of aniline as compared with the other isozymes of P-450. The ethanol-oxidizing activity of isozyme 3a, which requires the presence of NADPH and NADPH-cytochrome P-450 reductase and is stimulated by the presence of phosphatidylcholine, is not due to contamination by catalase or an NAD+-or NADP+-dependent alcohol dehydrogenase.

Acetaldehyde↗
PubMed1982

Catalytic activity of cytochrome P-450 isozyme 3a isolated from liver microsomes of ethanol-treated rabbits. Oxidation of alcohols.

Cytochrome P-450 isozyme 3a, isolated from hepatic microsomes of rabbits treated chronically with ethanol, was found to have a unique substrate specificity when compared with isozymes 2, 3b, 3c, and 4. Form 3a has unusually high activity in the p-hydroxylation of aniline and in the oxidation of alcohols to aldehydes. These properties are reflected in the increased activities of these substrates in microsomes from ethanol-treated rabbits as compared to microsomes from untreated animals or those administered phenobarbital or 5,6-benzoflavone. The ethanol-oxidizing activity of isozyme 3a, which requires the presence of NADPH and NADPH cytochrome P-450 reductase and is stimulated by the presence of phospholipid, was shown not to be due to contaminating catalase or an NAD- or NADP-dependent alcohol dehydrogenase. Isozyme 3a catalyzes the oxidation of methanol, 1-propanol, and 1-butanol as well as ethanol; the relationships between the apparent Km values for these alcohols and their octanol-water partition coefficients is in accord with the known hydrophobic nature of the P-450 binding site. Whereas typical substrates of isozyme 2 are known to be metabolized with the stoichiometry predicted of a monooxygenase reaction, with isozyme 3a the sum of acetaldehyde formed from ethanol and of hydrogen peroxide generated is inadequate to account for the NADPH and oxygen consumed. Free hydroxyl radicals appear to mediate the slow oxidation of ethanol in the presence of the reductase alone but not the faster rate catalyzed by P-450 isozyme 3a. The results obtained, however, do not rule out the involvement of hydroxyl radical equivalent generated and bound at the active site of the cytochrome.

Animals↗
PubMed1982

Purification and characterization of a unique isozyme of cytochrome P-450 from liver microsomes of ethanol-treated rabbits.

A new isozyme of cytochrome P-450 has been purified to electrophoretic homogeneity from hepatic microsomes of rabbits treated chronically with ethanol. Several criteria indicate that the ethanol-inducible cytochrome, which has a minimal molecular weight of 51,000 and is designated form 3a on the basis of its relative electrophoretic mobility, is distinct from the known isozymes of P-450. As judged spectrally, the new isozyme is high spin in the oxidized state, as is form 4, but differs in that the spin state is unperturbed by nonionic detergents. The absolute spectrum of the ferrous carbonyl complex of form 3a is red shifted as compared to that of forms 2, 3b, 3c, 4, and 6 and exhibits a maximum at 452 nm. The amino acid composition of form 3a is different from that of the other isozymes, and both the NH2- and COOH-terminal sequences are distinct; form 3a has an NH2-terminal alanine and a carboxyl-terminal leucine residue. Peptide mapping by sodium dodecyl sulfate-polyacrylamide gel electrophoresis following treatment with papain, chymotrypsin, or Staphylococcus aureus V8 protease and by high performance liquid chromatography following trypsinolysis indicates that form 3a is a unique gene product. This cytochrome displays the highest activity of all of the rabbit isozymes in the oxidation of ethanol to acetaldehyde and the p-hydroxylation of aniline when reconstituted with NADPH-cytochrome P-450 reductase and phospholipid in the presence of NADPH and oxygen.

Amino Acid Sequence↗