Biomedical subjects

Y Funae

Publications and source records attributed to Y Funae.

At least 109 records · Page 6Linked to original sources

PubMed1995

Inhibition and induction of cytochrome P450 isozymes after repetitive administration of imipramine in rats.

Repetitive oral administration of imipramine (100 mg/kg/day for 5 days) caused a decrease in rat liver microsomal debrisoquine 4-hydroxylase activity, a characteristic reaction catalyzed by cytochrome P450 (CYP) 2D1. Other CYP2D-dependent reactions (such as bunitrolol 4-hydroxylation, lidocaine 3-hydroxylation, and propranolol 4-, 5- and 7-hydroxylations) were also impaired by the treatment, but not those catalyzed by other CYP isozymes. Imipramine pretreatment did not change the immunochemically determined content of the CYP2D protein, suggesting that CYP2D is inactivated. Imipramine pretreatment also resulted in an increase in total CYP content and in formation of a ferrous CYP metabolic intermediate (MI)-complex absorbing at 454 nm. Although the total CYP content was increased by the treatment of these microsomes with ferricyanide to dissociate the MI-complex, the CYP2D-dependent activities were not restored, suggesting that the MI-complex was not the primary cause of CYP2D inhibition. This pretreatment regimen caused marked increases in immunochemically determined levels of CYP2A1, CYP2B1, CYP2B2, CYP2C6, and CYP3A2, and in the activities of 2 alpha-, 2 beta-, 6 beta-, 7 alpha-, 16 alpha-, and 16 beta-hydroxylation and 17-oxidation of testosterone. These results indicate that imipramine has two actions on the liver CYP system (i.e. as an inhibitor of the CYP2D enzyme and as a phenobarbital-type inducer).

Adrenergic beta-Antagonists↗

PubMed1994

Induction of cytochrome P450 isozymes in rat renal microsomes by cyclosporin A.

To examine the effects of cyclosporin A (CsA) on renal cytochrome P450 forms, CsA was administered to rats, and the renal levels of P450 were determined by immunoblotting. CsA treatment for 17 days increased total renal P450 content by 40% with a concomitant elevation of the omega- and (omega-1)-hydroxylation activities of lauric acid. Arachidonic acid omega-hydroxylation activity was also induced 2-fold by treatment with CsA for 17 days. Among the P450 forms, CYP4A2 was induced significantly, whereas CYP2C23, CYP4A1 and CYP4A8 were unaffected. These changes were accompanied by slight but significant increases in blood urea nitrogen and systolic blood pressure. These data suggest that CsA increased arachidonic acid omega-hydroxylation activity by the induction of CYP4A2. The specific induction of CYP4A2 may be related to CsA-induced nephrotoxicity and elevated blood pressure, because omega-hydroxyarachidonic acid is a potent vasoconstrictor.

Animals↗

PubMed1994

Occurrence of a P450 showing high homology to yeast lanosterol 14-demethylase (P450(14DM)) in the rat liver.

The rat liver cDNA library in lambda gt11 was screened with the antisera against rat liver lanosterol 14 alpha-demethylase (P450(14DM)), and one clone (pRT-9) was isolated. The open reading frame of pRT-9 cDNA showed high homology to yeast P450(14DM) (48.9% in nucleotides and 37.7% in amino acids). Homology of the heme-binding region of pRT-9 protein to that of yeast P450(14DM) was 80%. Three additional regions showing more than 60% homology were identified and one of them was assignable as the distal helix. These findings suggest that pRT-9 protein is P450(14DM) and P450(14DMs) of rat and yeast may be orthologous. This is the first evidence suggesting the occurrence of orthologous P450 in widely diverged species.

Amino Acid Sequence↗

PubMed1994

Differential roles of cytochromes P450 2D1, 2C11, and 1A1/2 in the hydroxylation of bufuralol by rat liver microsomes.

Bufuralol hydroxylation activities of liver microsomal cytochrome P450 (P450) enzymes were studied in the rat; the reaction has been used widely in determining levels of liver microsomal P450 2D6, which shows debrisoquine-type genetic polymorphism in humans. Liver microsomes catalyzed the conversion of bufuralol to 1'-hydroxybufuralol and a structurally unidentified metabolite (termed here as M-1) in the presence of an NADPH-generating system and molecular oxygen. Bufuralol 1'-hydroxylation activities catalyzed by the liver microsomes were not increased in rats treated with several P450 inducers, whereas beta-naphthoflavone treatment (and to a lesser extent that of isosafrole) caused a significant induction of M-1 formation. The major role of P450 1A1/2 in M-1 formation was confirmed by catalytic inhibition with anti-P450 antibodies and alpha-naphthoflavone in liver microsomes of beta-naphthoflavone-treated rats, and by reconstitution experiments containing P450 1A1 and 1A2. Among nine forms of purified rat P450 enzymes studied in the reconstituted system, P450 2C11 displayed the highest activities for bufuralol 1'-hydroxylation, followed by P450 1A1 and P450 2D1. A female-specific form of P450 2C12 did not catalyze bufuralol 1'-hydroxylation. In liver microsomes of male rats, however, P450 2D1 was the dominant enzyme because only anti-P450 2D1 antibodies, and not anti-P450 2C11 and anti-P450 1A1, inhibited the bufuralol hydroxylation activities, and a specific P450 2D1 inhibitor, quinine, caused a dramatic decrease in the hydroxylation activities. The major contribution of P450 2D1 in the bufuralol 1'-hydroxylation activities was also supported by a kinetic analysis of the reconstituted system; P450 2D1 enzyme had a very low Km value (8.4 microM) as compared with those of P450 2C11 (Km = 83 microM) and P450 1A1 (Km = 230 microM). Thus, the present results suggested that different P450 enzymes are involved in the hydroxylation of bufuralol in rat liver microsomes, and the kinetic analysis, as well as immunoinhibition and chemical inhibition experiments, may be of great importance for determining the major roles of P450 enzymes in drug hydroxylation reactions.

Adrenergic beta-Antagonists↗

PubMed1994

Metabolism of lidocaine by rat pulmonary cytochrome P450.

The metabolism of lidocaine was studied using microsomes from extrahepatic tissues of rats, including lung, kidney and brain, or using a reconstituted system with purified CYP2B1 and CYP4B. Rat pulmonary microsomes metabolized lidocaine to an N-deethylated metabolite, monoethylglycinexylidide (MEGX). Renal microsomes produced MEGX and 3-hydroxylidocaine (3-OH LID), although the rate of MEGX formation was much lower in renal than in pulmonary microsomes. Other metabolites were not detected. Lidocaine was not metabolized by brain microsomes. In extrahepatic tissues, pulmonary microsomes had the highest activity. Hence, two major forms of cytochrome P450 isozymes, CYP2B1 and CYP4B1, in rat pulmonary microsomes were used for further study. The study with a reconstituted system using purified cytochrome P450 isozymes revealed that only CYP2B1 showed lidocaine deethylation activity; the other form of cytochrome P450 in the lung, CYP4B1, did not. The Michaelis-Menten constant for lidocaine N-deethylation by rat pulmonary microsomes was 0.27 mM. Antibody against CYP2B1 completely inhibited the formation of MEGX by pulmonary microsomes. These results suggest that lidocaine is metabolized by rat lung, including CYP2B1.

Animals↗

PubMed1994

Metabolism of FK506, a potent immunosuppressive agent, by cytochrome P450 3A enzymes in rat, dog and human liver microsomes.

The oxidative metabolism of FK506 by liver microsomes and purified cytochrome P450 (P450) enzymes from rats, dogs and humans was studied. The major metabolite formed by liver microsomes from all species was 13-demethylated FK506, named M-I. In adult rats, liver microsomal metabolic activity toward FK506 was higher in males than in females and was stimulated by treatment with P450 3A inducers such as dexamethasone and phenobarbital. In a reconstituted monooxygenase system containing various forms of purified P450 3A enzymes, rat P450 3A2, dog P450 DPB-1 (a form of the P450 3A family) and human P450 3A4 catalyzed FK506 oxidation efficiently in the presence of cytochrome b5, a mixture of phospholipids (dilauroylphosphatidylcholine, dioleoylphosphatidylcholine and phosphatidylserine), and sodium cholate. Rat P450 2C6 and 2D1 and human P450 2CMP also metabolized FK506, with significant lower activity than the P450 3A enzymes, and other rat P450 1A, 2A, 2B, 2C and 2E families including C11 did not show catalytic activities for FK506. Anti-P450 3A2 and anti-P450 3A4 antibodies strongly inhibited FK506 oxidation catalyzed by rat and human liver microsomes, respectively. The formation rate of M-I correlated well with testosterone 2 beta- and 6 beta-hydroxylase activities in rat liver microsomes and with immunoquantified P450 3A4 content, nifedipine oxidase activity, and testosterone 6 beta-hydroxylase activity in human liver microsomes. These in vitro findings indicate that the P450 3A enzymes in liver microsomes from various species of animals, including human, play a major role in the first step oxidation of FK506.

Animals↗

PubMed1994

Trimethadione metabolism, a useful indicator for assessing hepatic drug-oxidizing capacity.

The metabolism of trimethadione (TMO), a useful indicator of hepatic drug-oxidizing capacity in rats and humans, was studied using 14 different forms of rat cytochrome P450 (CYP1A1, 1A2, 2A1, 2A2, 2B1, 2B2, 2C6, 2C7, 2C11, 2C12, 2C13, 2E1, 3A2 and 4A2) and three forms of human cytochrome P450 (CYP1A2, 2C and 3A4). TMO N-demethylation was increased by treating rats with phenobarbital. CYP2C11 and 2B1 had high TMO N-demethylase activity, but 1A1 and 1A2 had low activity. Antibodies raised to CYP2C11 and 2B1/2 inhibited TMO N-demethylation in hepatic microsomes of untreated and phenobarbital-treated rats, respectively. In a reconstituted system, human CYP3A4 and 2C produced efficiently dimethadione (DMO), but CYP1A2 did not catalyse TMO N-demethylation. Antibodies raised to CYP3A2 and 2C11 inhibited TMO N-demethylation in human hepatic microsomes. These results indicated that the N-demethylation of TMO is catalysed mainly by CYP2C11 and 2B1 in rat hepatic microsomes, and that human CYP3A4 and an unspecified isoform of the 2C subfamilies contribute to TMO N-demethylation in human liver.

Animals↗

PubMed1994

Changes in content of P450 isozymes in hepatic and renal microsomes of the male rat treated with cis-diamminedichloroplatinum.

1. The changes in the activity of drug-metabolizing enzymes and in the content of P450 isozymes in renal and hepatic microsomes after treatment of the male Sprague-Dawley rat with cis-diamminedichloroplatinum (Cisplatin, CDDP) were examined. 2. NADPH-P450 reductase activity in renal microsomes was significantly increased by treatment with CDDP, but lauric acid omega- and (omega-1)-hydroxylation activities of renal microsomes were not increased. 3. The level of P4502C23 was increased significantly and levels of P4504A2 and 4A8 tended to increase in renal microsomes. 4. In hepatic microsomes, lauric acid omega-hydroxylation activity was increased, but (omega-1)-hydroxylation activity was not. Levels of P4502C11 and 3A2, which are male-specific forms, were decreased, whereas levels of P4502A1, 2C7 and 2E1 were increased in hepatic microsomes. The levels of P4504A2 and 4A3 were increased by CDDP and the level of P4504A1 was not changed. Changes in the protein levels of P450 by CDDP were consistent with those in the mRNA levels reported previously (LeBlanc et al. 1992). 5. Male-specific forms in rat liver such as P4502C11 were decreased by CDDP, but those in the kidney such as P4504A2 was not. Therefore, CDDP has different influences on the regulation of hepatic and renal P450s.

Animals↗

PubMed1993

Regulation of renal cytochrome P450s by thyroid hormone in diabetic rats.

Effects of thyroid hormone treatment on renal P450 expression in the diabetic rats were investigated. Diabetes produced by streptozotocin induced CYP4A2 and P450 K-2 (similar form with CYP2C23) but not P450 K-4 (similar form with CYP4A8) and induced lauric acid hydroxylation activity. The serum thyroid hormone level was decreased with diabetes. Treatment of diabetic rats with thyroid hormone (T3) as well as with insulin reversed the increase in the levels of CYP4A2 and P450 K-2. Thyroidectomy also induced CYP4A2 and P450 K-2 in the rat kidney. The increase was reversed by treatment of thyroidectomized rats with T3. These findings suggest that expression of CYP4A2 and P450 K-2 in rat kidney is suppressively regulated by thyroid hormone and the decrease in thyroid hormone level in the diabetic state affects the levels of CYP4A2 and P450 K-2.

Animals↗

PubMed1993

Characterization of two P-450 isozymes placed in the rat CYP2D subfamily.

Two P-450s with debrisoquine 4-hydroxylation activity, designated P-450 UT-7 and UT-7b, were purified and partially purified, respectively, from hepatic microsomes of untreated male rats. Both purified P-450s with an apparent molecular weight of 49,000, were associated with another protein with an apparent molecular weight of 29,000 which was designated 29 k-protein. The CO-reduced spectra of both P-450 UT-7 and UT-7b showed a peak at 448 nm. The NH2-terminal amino acid sequences of P-450 UT-7 and UT-7b were the same as the amino acid sequences of CYP2D1 and CYP2D2 deduced from the cDNA, respectively, except for the lack of a terminal methionine for P-450 UT-7b. In a reconstituted systems, P-450 UT-7 and UT-7b catalyzed lidocaine 3-hydroxylation and N-deethylation in the presence of the 29 k-protein. The Km and Vmax values for lidocaine 3-hydroxylation were 3.6 microM and 0.50 nmol/min/nmol of P-450 for P-450 UT-7, and 3.6 microM and 0.93 nmol/min/nmol of P-450 for P-450 UT-7b, respectively. Antibody against P-450 UT-7, which also cross-reacted with P-450 UT-7b, inhibited lidocaine 3-hydroxylation in liver microsomes from untreated male rats, but had little effect on lidocaine N-deethylation. These findings suggested that lidocaine 3-hydroxylation in hepatic microsomes from untreated male rats was catalyzed by P-450 UT-7 and/or UT-7b.P-450 UT-7 not containing 29 k-protein was obtained as the non-absorbed fraction from hydroxylapatite HPLC. The activities of debrisoquine 4-hydroxylation as well as lidocaine 3-hydroxylation and N-deethylation in a reconstituted system with P-450 UT-7 without 29 k-protein were one-fifth of those of P-450 UT-7 containing 29 k-protein at the same substrate concentration. These findings suggested that the 29 k-protein was essential to express the maximal metabolic activities. However, the lidocaine metabolic activity in a reconstituted system with P-450 UT-7 containing 29 k-protein and in hepatic microsomes were not inhibited by 29 k-protein antibody.

Amino Acid Sequence↗

PubMed1993

Changes in amounts of cytochrome P450 isozymes and levels of catalytic activities in hepatic and renal microsomes of rats with streptozocin-induced diabetes.

Hepatic microsomal cytochrome P450s, which are involved in the metabolism of drugs, hormones, prostaglandins and fatty acids, change when animals develop diabetes. We studied changes in cytochrome P450 isozymes in both hepatic and renal microsomes of rats with diabetes caused by streptozocin, and compared the results with changes in catalytic activities in the microsomes. In hepatic microsomes of diabetic rats, the amount of cytochrome P450 2E1, an acetone-inducible isozyme, was two and a half times that of control rats, and that of P450 4A2, a major renal isozyme, was three times that in the controls. The amounts of cytochrome P450s 2A1, 2C6, 2C7, 3A2 and 4A3 increased in hepatic microsomes of diabetic rats, and P450 2C11 decreased. Treatment with insulin restored these to the levels in the controls. The catalytic activities of aniline hydroxylation, 7-ethoxycoumarin O-dealkylation, testosterone 2 beta, 6 beta, 7 alpha, and 16 beta-hydroxylation, and omega-, (omega-1)-hydroxylation of lauric acid were high in the hepatic microsomes of diabetic rats, and testosterone 2 alpha and 16 alpha-hydroxylation activities were low. In renal microsomes of diabetic rats, cytochrome P450s 2E1, 4A2 and K-4 were induced, and omega- and (omega-1)-hydroxylation activities were high. These changes were reversed by insulin treatment. The induction and suppression of cytochrome P450 isozymes in diabetic rats were consistent with the changes in the catalytic activities. In both hepatic and renal microsomes, P450s 2E1 and 4A2 were induced, altered metabolism of ketones and fatty acids in diabetes may contribute to these changes.

Animals↗

PubMed1993

Nicotine metabolism by rat hepatic cytochrome P450s.

Many kinds of cytochrome P450s were purified from rat hepatic microsomes, and their role in the metabolization of nicotine in a reconstituted system examined. Of four phenobarbital-inducible P450s, P450 2B1 had the highest nicotine oxidation activity and P450 2B2 showed a low rate of nicotine oxidation, whereas P450 2C6 and 3A2 had no detectable activity toward nicotine. Among eleven other purified cytochrome P450s tested, P450 2C11 had high nicotine oxidation activity and P450 1A2 and 2D1 showed low catalytic activity toward nicotine. The other cytochrome P450s, P450 1A1, 2A1, 2A2, 2C7, 2C12, 2C13, 2E1 and 4A1, had no detectable nicotine oxidation activity. Based on these results, participation of cytochrome P450s in nicotine metabolism in human and animal livers is discussed.

Animals↗

PubMed1993

Cytochrome P-450-butyl peroxide complex detected by ESR.

ESR measurements were performed for the reaction systems composed of t- or n-butylhydroperoxide and cytochrome P-450 (UT-2), purified from rat liver microsomes. On addition of n-butylhydroperoxide to the P-450 at pH 7.4, ESR signal due to a ferric low-spin species (g1 = 2.29, g2 = 2.24 and g3 = 1.96) was recorded. The observed g-parameters agreed well with those of a model thiolate-heme-iron(III)-peroxide complex, Fe(III)TPP(-S-TGE) (-OO-t-butyl) (g1 = 2.285, g2 = 2.198 and g3 = 1.959). In terms of the g-parameters, the new P-450 complex was concluded to be a P-450-butyl peroxide adduct, in which a butyl peroxide anion ligates at the sixth position of heme iron(III).

Animals↗

PubMed1993

Characterization of specific cytochrome P450 enzymes responsible for the metabolism of diazepam in hepatic microsomes of adult male rats.

The role of several P450 enzymes in the metabolism of diazepam (DZ) has been investigated. Hepatic microsomes of adult male rats were pretreated with antisera raised against the P450s CYP3A2, 2B1, 2C6, 2C11, 2D1 and 2E1, and their influence on the subsequent metabolism of DZ was determined by simultaneously measuring the changes in the relative rates of formation of its metabolites. Several forms of P450 were found to be positively involved in DZ metabolism. Antisera of the "male-specific" P450 enzyme CYP2C11 partially inhibited both DZ N-demethylase and C3 hydroxylase activities (60%) which resulted in decreased formations of N-desmethyl-DZ (NDZ) and 3-hydroxy-DZ (3HDZ), respectively. In a reconstitution experiment with the purified enzyme, CYP2C11 predominantly catalysed the formation of NDZ from DZ. Antisera of a further male-specific P450 CYP3A2 strongly inhibited (95%) the C3 hydroxylase of DZ and thus 3HDZ formation. A corresponding reconstitution experiment with this same P450 enzyme gave 3HDZ as principal product. CYP2D1 antisera inhibited the aromatic hydroxylation of DZ (98%) and subsequent formation of 4'-hydroxy-DZ (4'HDZ). This enzyme was also observed to inhibit DZ N-demethylase activity (60%). A reconstitution experiment with pure CYP2D1 catalysed the formation of both 4'HDZ and NDZ.

Animals↗

PubMed1993

Contribution of cytochrome P450s to MEOS (microsomal ethanol-oxidizing system): a specific and sensitive assay of MEOS activity by HPLC with fluorescence labeling.

The contribution of cytochrome P450s to MEOS (microsomal ethanol-oxidizing system) in rat hepatic microsomes was studied with a modified assay method for MEOS activity. Acetaldehyde produced by MEOS was converted into the fluorescent derivative with cyclohexane-1,3-dione and analyzed by HPLC with a fluorescence detector. Acetaldehyde production by hepatic microsomes of rats treated with ethanol was higher by 75% than that by control rats. Ethanol oxidation activity of eight forms of P450 was investigated in a reconstituted system. CYP1A2 and CYP2E1 had high rates of acetaldehyde formation. The Km value of CYP2E1 for ethanol oxidation was 9.48 mM, similar to that of hepatic microsomes from rats treated with ethanol. The Km value of CYP1A2 was higher than that of CYP2E1, indicating the CYP1A2 with lower affinity for ethanol compared with CYP2E1. From the results of an inhibition study with antibodies, CYP2E1 was found to be a main contributor to MEOS induced by ethanol in rats, but CYP1A2 was considered to play an important role for MEOS when CYP2E1 was not induced. These results present the possibility that CYP1A2 and CYP2E1 contribute to MEOS activity.

Acetaldehyde↗

PubMed1993

Expression of cytochrome P450 in LEC rats during the development of hereditary hepatitis and hepatoma.

The expression of 14 forms of cytochrome P450 in the liver as well as changes in the testosterone hydroxylation activities of hepatic microsomes were investigated during the development of hepatitis in Long-Evans Cinnamon (LEC) rats. P4501A1 and -1A2 (3-methylcholanthrene-inducible forms) and P4502B1 and -2B2 (phenobarbital-inducible forms) were barely detected in the hepatic microsomes of male and female LEC rats. In immature male rats, the levels of male-specific forms (P4502C11 and -2C13) were higher in LEC rats than in control Long-Evans Agouti (LEA) rats. P4502C11 appeared in female LEC rats from 4 to 16 weeks of age, reflecting that testosterone 2 alpha- and 16 alpha-hydroxylation activities were detected at significant levels in female LEC rats. In immature female rats, the level of P4502C12 (a major female-specific form) was higher in LEC rats than in LEA rats. The level of P4502C13 in male LEC rats and that of P4502C12 in female LEC rats decreased markedly with ageing or during the development of hepatitis. The level of P4503A2 (a male-predominant form) was especially high in immature male and female LEC rats, reflecting that both rats had high 2 beta- and 6 beta-hydroxylation activities toward testosterone. These sex-specific forms are regulated by androgens and by pituitary growth hormone. Thus, there may be abnormalities of the hypothalamo-pituitary-gonadal axis in LEC rats. Furthermore, P4503A2 efficiently activates aflatoxin B1, a potent hepatocarcinogen, and the increased levels of this form in LEC rats may be related to the onset of hepatitis or liver cancer.

Animals↗

PubMed1993

Increased CYP1A2 content and capacity to activate Glu-P-1 and Trp-P-2 in liver microsomes of scorbutic ODS rats.

Osteogenic Disorder Shionogi (ODS) rats, which cannot synthesize ascorbic acid due to a deficiency of L-gulonolactone oxidase, become scorbutic when not supplied with dietary ascorbic acid. We used the deficient rats to study the effects of ascorbic acid on the amount of cytochrome P450 enzymes in liver microsomes. The total amount of hepatic cytochrome P450 in ODS rats deprived of ascorbic acid was lower by approximately 40%, whereas ODS rats fed with ascorbic acid and the wild strain had the same level of total hepatic cytochrome P450. Western blot analysis for various forms of cytochrome P450 in liver microsomes indicated that the amount of CYP1A2 was significantly higher in ascorbic acid deficient rats. On the other hand, amounts of CYP2B2 and 3A were lower, and those of CYP2E1 and CYP2C6/11 were unaffected. In accordance with the higher amount of CYP1A2, Northern blot analysis showed increased expression of CYP1A2 mRNA. The capacity of microsomes to produce mutagens from 2-amino-6-methyl-dipyrido[1,2-a:3',2'-d]imidazole acetate (Glu-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole acetate (Trp-P-2) was higher in scorbutic ODS rats by the Ames test. These results indicate that the effects of ascorbic acid deficiency on the expression of cytochrome P450 in ODS rat livers are form-specific and that the increased CYP1A2 is associated with increased metabolic activation of promutagens in the scorbutic state.

Animals↗

PubMed1993

Mitochondrial NADPH-linked aquacobalamin reductase is distinct from the NADPH-linked enzyme from microsomal membranes in rat liver.

Mitochondrial NADPH-linked aquacobalamin reductase was purified and characterized to clarify its enzymatic properties. The enzyme was purified about 360-fold over rat liver mitochondrial membranes in a yield of 7.5%. The purified enzyme was homogenous in SDS-PAGE. The molecular mass (M(r)) of the enzyme was calculated to be 65 kDa by SDS-PAGE and by Toyopearl HW55 gel filtration, indicating that the enzyme is a monomeric polypeptide with M(r) of 65 kDa. The enzyme was a flavoprotein containing 1 mol of FAD and FMN per mole of the enzyme. The enzyme was specific for NADPH as electron donor and had the ability to reduce cytochrome c (15.4 mumol.min-1 x mg protein-1), potassium ferricyanide (4.9 mumol.min-1 x mg protein-1) and 2,6-dichlorophenolindophenol (16.8 mumol.min-1.mg protein-1) as well as aquacobalamin (6.4 mumol.min-1 x mg protein-1). Although the enzyme immunoreacted with an antibody against NADPH-cytochrome P-450 reductase, which had the activity of the NADPH-linked aquacobalamin reductase in rat liver microsomes, the mitochondrial enzyme and the microsomal enzyme had different enzymological properties.

Animals↗