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PubMed2001

Changes in mitochondrial and microsomal lipid peroxidation and fatty acid profiles in adrenal glands, testes, and livers from alpha-tocopherol-deficient rats.

Studies were done to evaluate the effects of alpha-tocopherol deficiency in rats on the fatty acid composition and sensitivity to lipid peroxidation (LP) of mitochondria and microsomes from adrenal glands, testes, and livers. In control (alpha-tocopherol-sufficient) animals, adrenal concentrations of alpha-tocopherol were approximately 10 times greater than those in livers and testes. Dietary deficiency of alpha-tocopherol for 8 weeks decreased adrenal and hepatic concentrations by 80-90% and testicular concentrations by approximately 60-70%. Incubation of testicular or hepatic mitochondria and microsomes from control rats with FeSO(4) (1.0 mM) caused a time-dependent stimulation of LP as indicated by the formation of thiobarbituric acid reactive substances (TBARS); the rate of TBARS production increased in preparations from alpha-tocopherol-deficient animals. TBARS formation was not demonstrable in adrenal mitochondria or microsomes from alpha-tocopherol sufficient rats, but reached high levels in alpha-tocopherol-deficient preparations. The fatty acid composition of mitochondria and microsomes was tissue-dependent. In particular, arachidonic acid comprised approximately 40% of the total fatty acids in adrenal membranes, but only 20-25% in testes and livers. alpha-Tocopherol deficiency increased oleic acid concentrations in adrenal and hepatic mitochondria and microsomes but not in testes. In all three tissues, linoleic acid concentrations decreased by approximately 50%, but arachidonic acid levels were unaffected by alpha-tocopherol deficiency. The results indicate a close relationship between tissue sensitivity to LP in vitro and alpha-tocopherol concentrations. Nonetheless, any oxidative stress in vivo caused by alpha-tocopherol deficiency seems to spare arachidonic acid in mitochondria and microsomes but decreases linoleic acid concentrations. It is possible that because of the important physiological functions of arachidonic acid, metabolic adaptations serve to maintain membrane content during periods of oxidative stress.

Adrenal Glands↗
PubMed2003

Studies on metabolic pathways of cocaine and its metabolites using microsome preparations from rat organs.

Cocaine metabolism has been studied previously with respect to the formation of predominant hydrolytic or hepatotoxic metabolites via oxidative pathways. In the present study, cocaine and eight of its metabolites (norcocaine, ecgonine methyl ester, benzoylecgonine, benzoylnorecgonine, 3-hydroxy-benzoylecgonine, cocaethylene, norcocaethylene, and ecgonine ethyl ester) were incubated with microsomes from rat liver, kidney, lung, and brain. Qualitative analysis of the metabolites produced was performed using solid phase extraction (SPE), trimethylsilylation, and GC/MS. It was found that the metabolites with a free carboxylic group (e.g., benzoylecgonine) were not further oxidized by microsomal enzymes and their presence in urine or blood may therefore be due to hydrolysis of the respective alkylated entities. Although microsomes from all organs exhibited oxidative metabolism, significant differences were noted. Kidney microsomes produced essentially the same results as liver, but aryl hydroxylated metabolites were not found in incubations with lung and brain microsomes. N-Hydroxy-norcocaine was found only in traces with brain microsomes. It appears that cocaine is converted to N-hydroxy-norcocaine (which is the precursor of toxic metabolites) not only in the liver but also in other organs of rat. This might be relevant in the development of lung toxicity observed in smokers of cocaine ("crack").

Animals↗
PubMed1965

THE SEQUENTIAL SYNTHESIS OF THE POLYPEPTIDE CHAIN OF SERUM ALBUMIN BY THE MICROSOME FRACTION OF RAT LIVER.

1. The isolated microsome fraction of regenerating rat liver was incubated with cell sap, a source of energy and [(35)S]methionine, [(14)C]isoleucine or [(14)C]leucine for different periods of time, and microsomal albumin isolated. 2. The distribution of these isotopes in albumin was determined by separation of tryptic peptides from the protein. Radioactivity was measured in peptides either qualitatively by radioautography or quantitatively by labelling with both (3)H and (14)C. 3. A gradient of radioactivity existed at all times in albumin isolated after incubating microsomes. 4. The shorter the incubation time the fewer the peptides labelled in albumin, but the peptides with highest specific activity after short incubation times corresponded to those with highest specific activities after long incubation times. 5. Leucine released from the C-terminus of albumin had a higher specific activity than the mean specific activity of the remaining leucine residues in albumin. 6. The peptide with the highest specific activity in albumin is probably derived from the C-terminus of the protein. 7. [(14)C]Glutamic acid is incorporated into the N-terminus of albumin after incubating the microsome fraction with this isotopically labelled amino acid, cell sap and a source of energy. The specific activity of the N-terminal glutamic acid under these conditions is less than the mean specific activity of the remaining glutamic acid and glutamine residues in albumin. 8. The results are interpreted as reflecting a sequential synthesis of serum albumin in the isolated microsome fraction of rat liver. The direction of synthesis of albumin is from the N-terminus towards the C-terminus. 9. The bulk of incorporation of radioactive amino acid into albumin in the isolated microsome fraction is due to completion of partially completed, pre-existing peptide and polypeptide chains. A limited synthesis of new chains of albumin does, however, occur.

Amino Acids↗
PubMed1983

Microsomal electron-transport reductase activities and fatty acid elongation in rat brain. Developmental changes, regional distribution and comparison with liver activity.

Gestational and postnatal changes of microsomal NADH:cytochrome b5 reductase and NADPH:cytochrome c reductase activities were examined in rat brain. The specific activity of NADH:cytochrome b5 reductase was high at 18-19 days of gestational age, decreased to a minimum at 4 to 6 days after birth and increased thereafter. An essentially similar developmental pattern was observed for the specific activity of NADPH:cytochrome c reductase. In contrast, the specific activities of these reductases in liver microsomes were low, did not display a peak during gestation and increased steadily to a maximum at 40-50 days after birth. The rate of incorporation of [2-14C]malonyl-CoA into palmitoyl-CoA in brain microsomes was found to be high in the foetus, sharply decreased to a minimum at the time of birth and increased thereafter. The activity of fatty acid elongation in liver microsomes was much less than that in brain during gestation and increased rapidly after birth to values at 50-60 days 20-fold greater than the foetal activity. NADH and NADPH were equally effective for brain microsomal fatty acid elongation. Regional distribution of cytochrome reductase activities and the activity of fatty acid elongation showed the lowest specific activity in cerebellum. These results suggest that brain microsomal electron transport may be correlated with the developmental alteration in fatty acid elongation.

Animals↗
PubMed2001

The glucuronidation of mycophenolic acid by human liver, kidney and jejunum microsomes.

AIMS: To estimate the relative contribution of liver, kidney and jejunum to MPA elimination via glucuronidation from in vitro kinetic data. METHODS: The kinetics of MPA glucuronidation by human liver, kidney and jejunum microsomes were characterized. Mycophenolic acid glucuronide (MPAG) concentrations in microsomal incubations were determined using a specific h.p.l.c. procedure. Non-specific microsomal binding of MPA was excluded using an equilibrium dialysis approach. RESULTS: Microsomes from all three tissues catalysed the conversion of MPA to MPAG. Mean microsomal intrinsic clearances for MPAG formation by liver, kidney and jejunum microsomes were 46.6, 73.5 and 24.5 microl (min mg)(-1), respectively. When extrapolated to the whole organ, however, hepatic intrinsic clearance was 21- and 38-fold higher than the respective intrinsic clearances for kidney and small intestine. CONCLUSIONS: The data suggest that the liver is the organ primarily responsible for the systemic clearance of MPA, with little contribution from the kidney, and that the small intestine would be expected to contribute to first-pass extraction to a minor extent only.

Glucuronates↗
PubMed1998

Fatty acid profiles and non enzymatic lipid peroxidation of microsomes and mitochondria from bovine liver, kidney, lung and heart.

The light emission = chemiluminescence and fatty acid composition, two markers of lipid peroxidation process, was evaluated in bovine liver, kidney, lung and heart microsomes and mitochondria incubated in the presence of ascorbate-Fe2+ at 37 degrees C. Microsomal and mitochondrial fractions obtained from lung, kidney and heart were more resistant to lipid peroxidation than those isolated from the liver. The ascorbate-Fe2+ seemed to be totally ineffective in stimulating peroxidation of bovine lung, heart and kidney microsomes or mitochondria. Whereas bovine liver microsomes or mitochondria displayed the highest values of chemiluminescence when incubated in the presence of ascorbate-Fe2+. The peroxidizability index a parameter that indicate the maximal rate of oxidation of specific fatty acids showed statistically significant differences in mitochondria isolated from lung heart and kidney and microsomes isolated from lung. The fatty acid profile of the subcellular fractions obtained from those tissues do not appear to be responsible for their different susceptibility to free radical degradation. Other factor/s may be responsible for the protection to lipid peroxidation observed in microsomal or mitochondrial fractions obtained from bovine lung, heart and kidney.

Animals↗
PubMed1999

Metabolism of tauromustine in liver and lung microsomes from various species.

1. The cytochrome P450 (CYP)-mediated metabolism of tauromustine has been evaluated in liver and lung microsomes from various species. Liver microsomes from rat pretreated with typical CYP inducers, human liver microsomes and cDNA-expressed human CYP enzymes were used to study the enzymatic basis of the metabolism. The further metabolism of the monodemethylated product of tauromustine and that of the denitrosated product were also investigated. 2. The major routes of tauromustine metabolism were demethylation to the alkylating active compound, R2, and denitrosation to the inactive metabolite, M3. The extent of metabolism and the activity of demethylation versus denitrosation varied among the species. The highest metabolism was found in mouse (BDF strain) followed by dog, rat and the human liver. Tauromustine was also metabolized to a low extent in lung microsomes from these species. 3. The further metabolism of R2 and M3 was approximately 100 times lower in activity than that of tauromustine. Both the demethylation and the denitrosation of tauromustine were increased 3-fold in liver microsomes from rat pretreated with phenobarbital, whereas treatment with cyanopregnenolone enhanced the denitrosation 11-fold, indicating the involvement of CYP3A. 4. Metabolism across a panel of 10 human liver microsomal samples demonstrated a correlation with testosterone 6beta-hydroxylation of demethylation (r2 = 0.86) and denitrosation of tauromustine (r2 = 0.79). Among the human cDNA expressed CYP enzymes, not only was tauromustine determined to be catalysed predominantly by CYP3A4, but also to some extent by CYP2C19 and CYP2D6. 5. In conclusion, the present results indicate a major role of CYP3A enzymes in the metabolism of tauromustine.

Animals↗
PubMed1963

Effect of trypsin on liver microsomes.

The effect of trypsin on the morphology of the rat liver microsomal fraction isolated by differential centrifugation has been investigated. The microsomes were incubated at 37 degrees C and centrifuged thereafter under the conditions of their initial isolation. The trypsin-treated microsomes and the untreated controls were fixed in unbuffered osmium tetroxide and embedded first in gelose and then in methacrylate. In the trypsin-treated microsomes, there was a removal of the ribosomes from the rough vesicles. Parallel chemical determinations showed that the total nitrogen and total phosphorus of the pellet were lowered. Particles, densely stained with phosphotungstic acid (PTA) and homogeneous in appearance, were found within microsome smooth vesicles in a fluffy layer which collects on the top of the microsome pellet. The morphology of these PTA-stained particles remained unchanged after incubation with trypsin.

Animals↗
PubMed1994

Evidence for a high-affinity enzyme in rat esophageal microsomes which alpha-hydroxylates N'-nitrosonornicotine.

The tobacco-specific nitrosamine N'-nitrosonornicotine (NNN) induces esophageal but not liver tumors in the rat. This may in part be due to tissue-specific differences in the activation of this nitrosamine. Therefore, the metabolism of NNN by microsomes from the mucosa of the rat esophagus was characterized and compared to its metabolism by liver microsomes. Esophageal microsomes metabolized NNN to both 4-hydroxy-1-(3-pyridyl)-1-butanone and 2-hydroxy-5-(3-pyridyl)tetrahydrofuran, the products of 2'- and 5'-hydroxylation of the pyrrolidine ring, respectively. This activity required an NADPH-generating system and was inhibited by carbon monoxide, suggesting that it is mediated by a cytochrome P450 enzyme. The apparent KM for total alpha-hydroxylation of NNN by esophageal microsomes was 49 +/- 6.5 microM and Vmax was 113 +/- 3.7 pmol/mg/min. The ratio of 2'-hydroxylation to 5'-hydroxylation was 3.2 +/- 0.5 when the NNN concentration was varied from 1 microM to 2 mM. 2'-Hydroxylation is believed to be the activation pathway responsible for the tumorigenicity of NNN. In contrast, the ratio of 2'- to 5'-hydroxylation of NNN by liver microsomes was between 0.71 and 0.23 depending on the concentration of NNN used. Hepatic microsomal metabolism of NNN was not saturated at 2 mM NNN, the highest concentration of NNN used. These results confirm the existence of an esophageal enzyme with high affinity for alpha-hydroxylation of NNN; it is probably a cytochrome P450. If this enzyme exists in the liver its activity is masked by high KM, high Vmax enzymes which also alpha-hydroxylate NNN. These enzymes are not present in the esophagus. The presence of a low KM esophageal enzyme that 2'-hydroxylates NNN is consistent with the hypothesis that NNN esophageal tumorigenicity is at least in part due to the efficient activation of NNN in this tissue.

Animals↗
PubMed2003

Comparative metabolism of N-nitrosopiperidine and N-nitrosopyrrolidine by rat liver and esophageal microsomes and cytochrome P450 2A3.

N-nitrosopiperidine (NPIP) is a potent esophageal carcinogen in rats whereas structurally similar N-nitrosopyrrolidine (NPYR) induces liver, but not esophageal tumors. NPIP is a possible causative agent for human esophageal cancer. Our goal is to explain mechanistically these differing carcinogenic activities in the esophagus. We hypothesize that differences in metabolic activation of these nitrosamines could be one factor accounting for their differing carcinogenicity. alpha-Hydroxylation is the key metabolic activation pathway leading to nitrosamine-induced carcinogenesis. In this study, we examined the alpha-hydroxylation rates of [3,4-(3)H]NPIP and [3,4-(3)H]NPYR by male F344 rat esophageal and liver microsomes. The major alpha-hydroxylation products of NPIP and NPYR, 2-hydroxytetrahydro-2H-pyran (2-OH-THP) and 2-hydroxytetrahydrofuran (2-OH-THF), respectively, were monitored by high performance liquid chromatography with radioflow detection. NPIP or NPYR (4 microM) was incubated with varying concentrations of esophageal microsomes and co-factors. Microsomes converted NPIP to 2-OH-THP with a 40-fold higher velocity than NPYR to 2-OH-THF. Similar results were observed in studies with NPIP and NPYR at substrate concentrations between 4 and 100 micro M. Kinetics of NPIP alpha-hydroxylation were biphasic; K(M) values were 312 +/- 50 and 1600 +/- 312 microM. Expressed cytochrome P450 2A3, found in low levels in rat esophagus, was a good catalyst of NPIP alpha-hydroxylation (K(M) = 61.6 +/- 20.5 microM), but a poor catalyst of NPYR alpha-hydroxylation (K(m) = 1198 +/- 308 micro M). Cytochrome P450 2A3 may play a role in the preferential activation of NPIP observed in rat esophagus. Liver microsomes metabolized NPYR to 2-OH-THF (V(max)/K(M) = 3.23 pmol/min/mg/ microM) as efficiently as NPIP to 2-OH-THP (V(max)/K(M) = 3.80-4.61 pmol/min/mg/ microM). We conclude that rat esophageal microsomes activate NPIP but not NPYR whereas rat liver microsomes activate NPIP and NPYR. These results are consistent with previous findings that tissue-specific activation of nitrosamines contributes to tissue-specific tumor formation.

Animals↗
PubMed1984

Activation of 2-amino-6-methyldipyrido[1,2-a:3' ,2' -d]imidazole, a mutagenic pyrolysis product of glutamic acid, to bind to microsomal protein by NADPH-dependent and -independent enzyme systems.

The conversion of 2-amino-6-methyldipyrido[1,2-a:3' ,2' -d]-imidazole (Glu-P-1), a highly mutagenic principle in a pyrolysate of glutamic acid, to protein-bound metabolites in vitro was examined with microsomes from various tissues of female F344 rats. Addition of NADPH to the incubation mixture containing microsomes and [14C]Glu-P-1 increased the binding of its metabolites to microsomal proteins linearly with time for up to 30 min, while on addition of arachidonic acid the binding increased linearly only for the first 2-4 min of incubation and then levelled off. However, due to the initial rapid binding, addition of arachidonic acid resulted in 6-fold greater binding of metabolites to small intestinal microsomes than addition of NADPH on incubation for 4 min, and with microsomes from liver and colon, arachidonic acid was found to be a better cofactor than NADPH for activation of Glu-P-1. Indomethacin significantly inhibited the increase in binding by arachidonic acid. Additions of linoleic and linolenic acids also increased the binding, but addition of oleic acid had no influence. With hepatic microsomes from 3-methylcholanthrene-treated rats, binding within 4 min after addition of arachidonic acid was greater than that after addition of NADPH and the reverse on further incubation. These findings suggest that prostaglandin synthetase may serve as an alternative enzyme to cytochrome P-450 monooxygenases for conversion of Glu-P-1 to active intermediates in all the rat tissues investigated.

Animals↗
PubMed1985

Covalent binding of diethylstilbestrol to microsomal protein in vitro correlates with the organotropism of its carcinogenicity.

[14C]Diethylstilbestrol (DES) was incubated in vitro with liver and kidney microsomes from male and female hamsters and rats, and the extent of non-extractable binding of radioactivity to microsomal protein was determined. Binding to microsomes from male hamster kidney, which is a target organ for DES carcinogenicity in vivo, was found to be 5-10 times higher than binding to microsomes from non-target tissues. Pretreatment with phenobarbital led to a marked increase in binding of DES to kidney microsomes but not to liver microsomes from female hamsters and male and female rats. The correlations of in vitro covalent binding with organ susceptibility implies a role for metabolic activation of DES in the mechanism of its carcinogenicity.

Animals↗
PubMed1996

Lanosterol 14-demethylase activity expressed in rat brain microsomes.

The occurrence of sterol 14-demethylase in rat brain microsomes was confirmed. The brain microsomes from adult rats converted lanosterol into its 14-demethylated products, 4,4-dimethylcholesta-8, 24-dienol, and 4,4-dimethylcholesta-8,14,24-trienol, in the presence of NADPH and molecular oxygen. This metabolism of lanosterol was inhibited by carbon monoxide and ketoconazole, a potent inhibitor of sterol 14-demethylase P450 (P45014DM or CYP51). These facts indicated the occurrence of lanosterol 14-demethylation in rat brain microsomes and its dependency on P45014DM. A representative value of the lanosterol demethylase activity of the brain microsomes was 8.4 pmol/min/mg protein or 640 pmol/ min/nmol of total P450. The former was about one-thirteenth of the corresponding value observed with liver microsomes from the same rats, while the latter was 4-times higher than the corresponding value obtained with the liver microsomes. This fact suggested that the ratio of P45014DM to other P450 species was higher in brain than in liver. Lanosterol 14-demethylation is situated at the root of the sterol-biosynthetic branch of the mevalonic acid pathway. Therefore, the present finding enzymologically supports the existence of the sterol biosynthetic pathway in brain.

Animals↗
PubMed1986

Effect of peroxisomal proliferators on microsomal prostaglandin A omega-hydroxylase.

Earlier, we reported the isolation of a cytochrome P-450 highly active in prostaglandin A (PGA) omega-hydroxylation (PGA omega-hydroxylase) from rabbit kidney cortex, small intestine, and colon microsomes. In the present studies, the effects of peroxisomal proliferating agents on the PGA omega-hydroxylase have been examined. Administration of clofibrate or di(2-ethylhexyl)phthalate (DEHP) resulted in a significant increase in the PGA1 omega-hydroxylase activity of kidney cortex, liver, and small intestine microsomes. Similar findings were also obtained for laurate hydroxylase activity in kidney and liver microsomes. Kidney PGA omega-hydroxylase (designated cytochrome P-450ka) was isolated and highly purified from clofibrate- or DEHP-treated rabbits, with a yield 3 times higher than that from untreated, or phenobarbital- or 3-methylcholanthrene-treated rabbits. Cytochrome P-450ka from clofibrate- or DEHP-treated rabbits exhibited the same properties as those from untreated rabbits. Guinea pig antiserum against cytochrome P-450ka strongly inhibited the omega-hydroxylation of PGA1 by kidney cortex microsomes from clofibrate-treated rabbits. The PGA1 omega-hydroxylase activity of clofibrate-treated liver microsomes was also inhibited by this antiserum, suggesting that a PGA omega-hydroxylase immunochemically related to cytochrome P-450ka exists in liver microsomes.

Animals↗
PubMed1981

Some properties of a hexadecane hydroxylation system in rabbit intestinal mucosa microsomes.

Among many different tissues of rabbit, hexadecane hydroxylation activity was found in only small intestine and liver microsomes. Both activities for hexadecane and decane hydroxylation in intestinal microsomes were significantly higher than those in liver microsomes. In contrast, the hydroxylation activities of p-xylene, benzo(a)pyrene, and decanol, and the demethylation activity of aminopyrine in the former were much lower than those in the latter. The intestinal microsomes converted [1-14C]hexadecane to cetyl alcohol, but not further to palmitic acid. Hexadecane hydroxylation activity was found to be markedly stimulated by non-ionic detergents such as Triton X-100, Nonident P-40, and Emulgen 913. Phosphatidylcholine and phosphatidylethanolamine stimulated the activity to a lesser extent. The hydroxylation was inhibited by various aliphatic hydrocarbons with carbon numbers larger than 10, but not by aromatic and polycyclic hydrocarbons. Hexadecane hydroxylation activity was solubilized from the intestinal microsomes and reconstituted with a partially purified cytochrome P-450 fraction, and intestinal NADPH-cytochrome c reductase, or spinach ferredoxin and ferredoxin-NADP reductase. The chromatography of the crude cytochrome P-450 preparation on hydroxylapatite separated at least two cytochrome P-450 fractions; one preferentially hydroxylating hexadecane, and the other preferentially hydroxylating myristic acid. The results suggest that rabbit intestinal mucosa microsomes had a cytochrome P-450 species specialized for hexadecane hydroxylation.

Alkanes↗
PubMed1991

Cyclosporine A metabolism by cytochrome P-450III occurs in microsomes from rat liver but not from normal epidermis or psoriatic lesions.

Cyclosporine A is efficacious in the treatment of psoriasis when taken orally or injected intralesionally but not topically. Lack of penetration to necessary locations or rapid metabolism during passage through the epidermis may account for the ineffectiveness. Cytochromes P-450III in the liver are known to be involved in cyclosporine metabolism and inactivation. This study was undertaken to determine if an epidermal cytochrome P-450III exists that can inactivate topical cyclosporine A. Rats were treated with the macrolide antibiotic erythromycin to induce the cytochrome P-450III family of enzymes. Microsomal fractions were prepared from liver and epidermis of rats and from lesional areas of psoriasis patients. NADPH cytochrome C reductase activity was determined as a positive control for microsomal enzymatic activity. Formation of metabolite 1, the predominant metabolite of cyclosporine A, by liver microsomes was increased 193% after 10 d erythromycin treatment. The cytochrome P-450 dependent activity in microsomes from the epidermis of control and erythromycin-treated rats and in microsomes from psoriatic tissue was at the detection limits of the assay system. Cytochrome P-450III gene family mRNA were detectable by polymerase chain reaction in liver but not in psoriatic or normal epidermis. The lack of detectable P-450III mRNA and the absence or minimal conversion of cyclosporine A to inactive metabolites by epidermal microsomes suggest that the ineffectiveness of topical cyclosporine A in psoriasis may not be due to inactivation of cyclosporine A by cytochrome P-450 in the skin.

Animals↗
PubMed1982

Identification of ribophorins in rough microsomal membranes from different organs of several species.

Microsomes prepared from several animal sources were analyzed for the presence of proteins corresponding to the ribophorins (I and II) which have been previously characterized in rat liver rough microsomes and appear to be involved in the binding of polysomes to endoplasmic reticulum membranes. In rough microsomal membranes from rat lacrimal gland, rabbit liver, dog and chicken pancreas, and mouse myeloma, ribophorin-like polypeptides with similar electrophoretic mobilities were detected by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. In all cases the polypeptides remained associated with sedimentable polysomes after solubilization of the microsomal membranes with nonionic detergents. Ribophorin-like polypeptides were absent from smooth microsomes. Antibodies raised against each rat liver ribophorin, purified by preparative sodium dodecyl sulfate/polyacrylamide gel electrophoresis, immunoprecipitated only the corresponding polypeptide, indicating no crossreactivity between ribophorins I and II. These antibodies also immunoprecipitated the homologous ribophorins found in microsomal preparations from other organs and species.

Animals↗
PubMed1982

Monooxygenase activities of human liver, lung, and kidney microsomes - a study of 42 post mortem cases.

The cytochrome P-450-dependent monooxygenase system was examined in microsomal fractions prepared from 42 post mortem human livers and 9 lungs and kidneys. Electron microscopy studies indicated that the human liver samples were relatively free of mitochondrial and plasma membrane contamination, but samples of kidney and lung were less pure. The microsomal fractions from all organs were judged to be relatively free of haemoglobin and methaemoglobin. The specific enzyme activities for several drug substrates for the monooxygenase, NADPH-cytochrome c reductase activity and the content of the microsomal cytochromes were measured. The values of the biochemical parameters studied were found to be quite variable and the values for the human liver were appreciably lower than those obtained with liver microsomes from laboratory rodents. The enzyme activities of the human kidney and lung microsomal fractions were 1-10% of those seen for human liver samples, except for NADPH-cytochrome c(P-450) reductase activity. In order to evaluate any post mortem changes in human liver, correlations between drug metabolism activities and either cytochrome P-450 or NADPH-cytochrome c (P-450) reductase content were examined. Strong correlations (r greater than 0.91) were seen only between aminopyrine or ethylmorphine demethylase activity and cytochrome P-450 content in samples obtained within 4 hours of death. Longer post mortem times gave poorer correlation between activity and cytochrome content. These studies document several conditions required in order to obtain human microsomal fractions representative of the activities in fresh, viable tissue.

Adult↗