Major antigen of liver kidney microsomal autoantibodies in idiopathic autoimmune hepatitis is cytochrome P450db1

Type 1, liver kidney microsomal autoantibodies (LKM-1) are associated with a subgroup of idiopathic autoimmune type, chronic active hepatitis (CAH). The antigenic specificity of LKM-1 autoantibodies from 13 patients was investigated by immunoblot analysis of human liver microsomal proteins. Polypeptides of 50, 55, and 64 kD were detected with these antisera. A high titer LKM-1 serum was selected to screen a human liver lambda gt11 cDNA expression library, resulting in the isolation of several complementary (c)DNA clones. Autoantibodies affinity purified from proteins expressed by two of the immunopositive cDNA clones, HLD8.2 and HLD13.2, specifically react with a 50-kD protein of human liver microsomes and display immunofluorescence staining of the proximal renal tubular epithelia characteristic of LKM-1 sera. Determination of the sequence of HLD8.2 revealed that it encodes a recently described cytochrome P450db1. A bacterial fusion protein constructed from HLD8.2 proved to be a specific and sensitive diagnostic reagent. All sera from patients with LKM-1 positive liver disease react with this fusion protein. No reaction was seen, however, for sera from patients with other types of autoimmune liver diseases, viral hepatitis, systemic immunological disorders, or healthy controls.

Evidence for cytochrome P-450NF, the nifedipine oxidase, being the principal enzyme involved in the bioactivation of aflatoxins in human liver

In vitro studies with human liver indicate that the major catalyst involved in the bioactivation of the hepato-carcinogen aflatoxin B1 (AFB1) to its genotoxic 2,3-epoxide derivative is cytochrome P-450NF (P-450NF), a previously characterized protein that also catalyzes the oxidation of nifedipine and other dihydropyridines, quinidine, macrolide antibiotics, various steroids, and other compounds. Evidence was obtained using activation of AFB1 as monitored by umuC gene expression response in Salmonella typhimurium TA1535/pSK1002 and enzyme reconstitution, immunochemical inhibition, correlation of response with levels of P-450NF and nifedipine oxidase activity in different liver samples, stimulation of activity by 7,8-benzoflavone, and inhibition of activity by troleandomycin. Similar results were obtained when levels of 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 formed in DNA were measured. P-450NF or a closely related protein also appears to be the major catalyst involved in the activation of aflatoxin G1 and sterigmatocystin, the latter compound being more genotoxic than AFB1 in these systems. Several drugs and conditions are known to influence the levels and activity of P-450NF in human liver, and the activity of the enzyme can be estimated by noninvasive assays. These findings provide a test system for the hypothesis that a specific human disease state (liver cancer) is linked to the level of oxidative metabolism in populations in which aflatoxin ingestion is high.

Immunochemical and catalytical studies on hepatic coumarin 7-hydroxylase in man, rat, and mouse

The cytochrome P-450-mediated coumarin 7-hydroxylase (COH) was studied in microsomal preparations from Wistar rat, DBA/2N mouse, and human liver. Human liver contained the highest constitutive COH activity of up to about 500 pmol/mg microsomal protein/min. The rat liver contained low levels of COH (about 3-5 pmol/mg protein/min) which could be demonstrated only with high substrate concentrations. Rabbit polyclonal antibody generated against P-450Coh (a P-450 isozyme purified from pyrazole-treated DBA/2N mouse liver showing high activity for coumarin 7-hydroxylation) inhibited COH activity by almost 100% in human liver microsomes and 86-99% in mouse liver microsomes. Also the deethylation of 7-ethoxycoumarin was inhibited somewhat by the antibody, whereas no inhibition was obtained in ethoxyresorufin O-deethylase and aryl hydrocarbon hydroxylase activities. None of these enzyme activities was affected by the antibody in the rat liver microsomes. In Ouchterlony immunodiffusion analysis precipitin lines were obtained with human, mouse and rat liver microsomes. Complex coalescence patterns were obtained suggesting full identity between human and pyrazole-treated mouse antigens, partial identity between mouse and rat antigens, and no identity between human and rat antigens. Western blot analysis with the anti-P-450Coh antibody revealed a distinct 48-kDa protein in all four human samples tested. A 50-kDa protein comigrating exactly with P-450Coh was observed in microsomes from PB and pyrazole-treated mouse liver microsomes. No distinct protein bands appeared in rat liver samples. These data suggest that despite slightly differing molecular masses, the human and mouse P-450s supporting COH are structurally conserved at their active centers. The corresponding rat P-450 appears to differ from that of mouse and man.

Characterization of cDNAs, mRNAs, and proteins related to human liver microsomal cytochrome P-450 (S)-mephenytoin 4'-hydroxylase

A cytochrome P-450 (P-450) multigene family codes for several related human liver enzymes, including the P-450 responsible for (S)-mephenytoin 4'-hydroxylation. This enzyme activity has previously been shown to be associated with a genetic polymorphism. Genomic (Southern) blot analysis using non-overlapping 5' and 3' portions of a cDNA clone suggests that approximately seven related sequences are present in this gene family. In this study four cDNA clones, all nearly full-length, were isolated from a bacteriophage lambda gt11 library prepared from a single human liver. These clones can be grouped into two categories that are approximately 85% identical at the level of DNA sequence. The cDNA clones in one category (MP-4, MP-8) both match the N-terminal sequences of the P-450MP-1 and P-450MP-2 proteins, which had previously been shown to be catalytically active in (S)-mephenytoin 4'-hydroxylation. These two cDNAs, MP-4 and MP-8, differ in only two bases in the coding region but are quite distinct in their 3' noncoding regions. Another protein (P-450MP-3) was isolated on the basis of its immunochemical similarity to P-450MP-1 but was found to be catalytically inactive; amino acid sequencing of tryptic peptides of P-450MP-3 showed a correspondence to the second category of cDNA clones (MP-12, MP-20), which differ from each other in only four (nonsilent) base changes. Oligonucleotides specific for the two groups of cDNA clones were used as probes of human liver mRNAs--individual liver samples examined expressed both types of mRNAs but no correlation was observed between the abundance levels of any mRNA and catalytic activity. Further, oligonucleotide probes indicated that mRNAs corresponding to both the MP-4 and MP-8 clones were apparently present in individual liver samples. A monoclonal antibody was isolated that recognized P-450MP-1 but not P-450MP-2 or P-450MP-3; the amount of protein detected by the antibody in different liver samples was not correlated with the mephenytoin 4'-hydroxylase activity. These results indicate that several closely related P-450 genes are all expressed in individual human livers. The MP-4/MP-8 gene products are proposed to be the ones most likely involved in mephenytoin 4'-hydroxylation, and much of the variation in catalytic activity among individuals is not a result of differences in levels of P-450MP-1 or mRNA but may be due to base differences in the structural gene(s).

Polyclonal and monoclonal antibodies to human lysyl hydroxylase and studies on the molecular heterogeneity of the enzyme

Human placental lysyl hydroxylase gave two bands in SDS/polyacrylamide-slab-gel electrophoresis: a broad, diffuse, major band corresponding to an apparent Mr of 80,000-85,000, and a sharp minor band with Mr 78,000. Mouse and chick-embryo lysyl hydroxylases gave only the broad, diffuse band, whereas the sharp band could not be detected. Polyclonal antibodies were prepared to the two bands of the human enzyme separately, and monoclonal antibodies were prepared to the whole purified enzyme preparation. Both types of polyclonal antibody inhibited and precipitated the enzyme activity, and both stained the two polypeptide bands in immunoblotting after SDS/polyacrylamide-gel electrophoresis. Only one out of five monoclonal antibodies inhibited the enzyme activity, whereas they all precipitated the activity when studied with antibody coupled to Sepharose. All five monoclonal antibodies stained the whole broad band in immunoblotting, and at least three of them also stained the sharp band. Peptide maps produced from the two polypeptide species by digestion with Staphylococcus aureus V8 protease were highly similar. Experiments with endoglycosidase H demonstrated that the Mr-80,000-85,000 polypeptide contains asparagine-linked carbohydrate units, which are required for maximal lysyl hydroxylase activity. The data suggest that the lysyl hydroxylase dimer consists of only one type of monomer, the heterogeneity of which is due to differences in glycosylation.

Macrolide antibiotic biosynthesis: isolation and properties of two forms of 6-deoxyerythronolide B hydroxylase from Saccharopolyspora erythraea (Streptomyces erythreus)

A cytochrome P-450 monooxygenase that catalyzes the hydroxylation of 6-deoxyerythronolide B, an intermediate of erythromycin A biosynthesis in Saccharopolyspora erythraea (formerly Streptomyces erythreus), was resolved into two forms, P-450I and P-450II, by hydroxylapatite chromatography. These two proteins were purified to homogeneity from the CA 340 strain and found to have a P-450 content of 17.5 and 15.2 nmol/mg of protein, respectively. Either enzyme catalyzed the NADPH-dependent hydroxylation of 6-deoxyerythronolide B and (9R)- or (9S)-9-deoxo-9-hydroxy-6-deoxyerythronolide B in vitro when reconstituted with other electron-transport components from S. erythraea. Both of them had a Mr of 44,220 +/- 1350, a pI of 4.6, similar amino acid compositions, and an identical N-terminal sequence for the first five amino acids. They also showed identical antigenicity and cross-reactivity against polyvalent and specific antibodies and contained cytochrome P-450 in the low spin state with absorption maxima at 416, 532, and 565 nm. Their distinguishing characteristics were different activities toward the (9S)-9-deoxo-9-hydroxy-6-deoxyerythronolide B substrate and slightly different absorbance maxima in their dithionite-reduced CO-complexed spectra.

Protein-protein interactions and antigenic relationships between the components of 4-methoxybenzoate monooxygenase and of benzene 1,2-dioxygenase from Pseudomonas putida

The investigations presented in this paper were performed on two enzyme systems from Pseudomonas putida: (a) 4-methoxybenzoate monooxygenase, consisting of a NADH: putidamonooxin oxidoreductase and putidamonooxin, the oxygen-activating component, and (b) benzene 1,2-dioxygenase, a three-component enzyme system with an NADH: ferredoxin oxidoreductase, functioning together with a plant-type ferredoxin as electron-transport chain, and an oxygen-activating component similar to putidamonooxin in its active sites. The influence of temperature, ionic strength, and pH on the activities of 4-methoxybenzoate monooxygenase and of NADH: putidamonooxin oxidoreductase were investigated. The studies revealed that the activity of 4-methoxybenzoate monooxygenase is determined by the behaviour of the reductase. Spectroscopic measurements showed that the interaction between the two components of 4-methoxybenzoate monooxygenase influences the optical-absorption behaviour of one or both components. As a criterion for the affinity between the two components of 4-methoxybenzoate monooxygenase, the Km value of the reductase for putidamonooxin was determined and found to be 31 +/- 11 microM. Antibodies against both components of 4-methoxybenzoate monooxygenase were obtained from rabbits. The antibodies against putidamonooxin inhibited the O-demethylation reaction (up to 80%) and also the reduction of putidamonooxin by the reductase (up to 40%). The antibodies against putidamonooxin did not interact with the oxygen-activating component of benzene 1,2-dioxygenase. The electron-transport chains of 4-methoxybenzoate monooxygenase and benzene 1,2-dioxygenase could not be replaced by one another without a complete loss of enzyme activity.

Selective induction of coumarin 7-hydroxylase by pyrazole in D2 mice

Pyrazole, was given to DBA/2N (D2), C57BL/6N (B6) and AKR/N mice to study its effects on hepatic drug metabolism. A decrease in the total amount of microsomal cytochrome P-450 as well as in the activities of ethylmorphine demethylase and benzo[a]pyrene hydroxylase was found. On the other hand ethoxycoumarin de-ethylase was increased 1.5-2.5-fold (depending on the strain of mouse) and coumarin 7-hydroxylase as much as sevenfold (but only in D2 mice) after pyrazole treatment. This increase was much higher than that caused by phenobarbital, the only well known inducer of coumarin 7-hydroxylase. By reconstituting the mono-oxygenase complex after purification of cytochrome P-450 we found a 40-fold increase in coumarin 7-hydroxylase and eightfold increase in ethoxycoumarin de-ethylase after pyrazole treatment. This was found only in D2 mice. An antibody previously developed against a cytochrome P-450 fraction from the the D2 strain with a high coumarin 7-hydroxylase activity inhibited the microsomal coumarin 7-hydroxylase almost 100% after pyrazole pretreatment of the animals. In the case of control or phenobarbital-treated mice the inhibition was somewhat weaker. With the reconstituted mono-oxygenase complex the inhibition of coumarin 7-hydroxylase was almost 100% both for control and pyrazole-treated D2 mice. The data indicate that pyrazole causes an induction of the microsomal monooxygenase complex different from that caused by phenobarbital or 3-methylcholanthrene and selective for coumarin 7-hydroxylation or 7-ethoxycoumarin de-ethylation. This induction was strong in D2, weak in B6 and absent in AKR/N mice.

Quantification of cytochrome P-450-dependent cyclohexane hydroxylase activity in normal and neoplastic reproductive tissues

It is well established that liver microsomal cytochrome P-450 participates in steroid metabolism and probably also in the metabolism of anti-oestrogens such as tamoxifen (Nolvadex). Thus it is possible that variations in cytochrome P-450 levels may influence the responsiveness of human breast and endometrial carcinomas to endocrine therapy. Therefore a simple sensitive spectrophotometric assay for determining levels of cytochrome P-450-dependent cyclohexane hydroxylation activity in breast and uterine microsomes (microsomal fractions) has been developed. Cyclohexane was chosen as a substrate because of the relatively high levels of cyclohexane hydroxylase activity in tumour microsomes and because cyclohexane serves as a substrate for several forms of cytochrome P-450. As previously described [Senler, Dean, Pierce & Wittliff (1985) Anal. Biochem. 144, 152-158], a direct method utilizing isotope-dilution/gas chromatography-mass spectrometry was also developed in order to confirm the results of the spectrophotometric assay. The average activity (cyclohexane-dependent NADPH oxidation) for 139 human breast-tumour microsome preparations was 1.34 nmol/min per mg, which is in the range of that found in untreated mammalian liver (1-3 nmol/min per mg). Also, high enzyme activity was demonstrated in human ovary, normal uterus as well as uterine leiomyomas. Endocrine status appeared to influence enzyme levels, in that mammary tissue from virgin rats contained significantly (P less than 0.025) higher amounts of activity than did tissues from either pregnant or lactating rats. Furthermore, carbon monoxide, as well as an antibody against rat liver cytochrome P-450, completely inhibited NADPH oxidation by breast-carcinoma microsomes. These results strengthen our hypothesis that tumours with high levels of cytochrome P-450 may have a reduced response to additive endocrine therapy.

Purification and characterization of a microsomal cytochrome P-450 with high activity of coumarin 7-hydroxylase from mouse liver

Phenobarbital-induced coumarin 7-hydroxylase is high in DBA/2J and low in C57BL/6N inbred mice; this genetic difference is encoded by the Coh locus on chromosome 7. The aim of this study was to develop an antibody specific for this cytochrome P-450 polymorphism. P-450 fractions, highly specific for phenobarbital-inducible coumarin 7-hydroxylase activity, were purified from DBA/2J and C57BL/6N mouse liver microsomes. Both proteins are 49 kDa, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Soret peaks of the reduced cytochrome . CO complexes are 451 nm. Reconstituted DBA/2J coumarin 7-hydroxylase activity exhibits a V twice as high as, and a Km value 10-fold less than, the reconstituted C57BL/6N activity. Antibodies were raised in rabbit. By Ouchterlony immunodiffusion, both antibodies show 100% cross-reactivity with DBA/2J and C57BL/6N microsomes and purified antigens. Yet, DBA/2J but not C57BL/6N 7-hydroxylase activity is inhibited by the antibody to DBA/2J P-450. Both DBA/2J and C57BL/6N activities are blocked by the antibody to C57BL/6N P-450. Neither antibody has any effect on liver microsomal d-benzphetamine N-demethylase, ethylmorphine N-demethylase, aminopyrine N-demethylase, 7-ethoxycoumarin O-deethylase, acetanilide 4-hydroxylase, or aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity. The DBA/2J protein most specific for phenobarbital-induced coumarin 7-hydroxylation is designated 'P-450Coh'. Anti-(P-450Coh) precipitates a relatively minor 49-kDa protein from detergent-solubilized microsomes and from in vitro translation of poly(A+)-enriched total RNA of phenobarbital-treated DBA/2J mouse liver, whereas the major phenobarbital-induced P-450 proteins exhibit a molecular mass of about 51 kDa. The immunoprecipitated translation products correspond to a messenger RNA of 2100 +/- 100 nucleotides.

Immunological characterization of lysyl hydroxylase, an enzyme of collagen synthesis

Antibodies to pure lysyl hydroxylase from whole chick embryos were prepared in rabbits and used for immunological characterization of this enzyme of collagen biosynthesis. In double immunodiffusion a single precipitation line was seen between the antiserum and crude or pure chick-embryo lysyl hydroxylase. The antiserum effectively inhibited chick-embryo lysyl hydroxylase activity, whether measured with the biologically prepared protocollagen substrate or a synthetic peptide consisting of only 12 amino acids. This suggests that the antigenic determinant was located near the active site of the enzyme molecule. Essentially identical amounts of the antiserum were required for 40% inhibition of the same amount of lysyl hydroxylase activity units from different chick-embryo tissues synthesizing various genetically distinct collagen types. In double immunodiffusion a single precipitation line of complete identity was found between the antiserum and the purified enzyme from whole chick embryos and the crude enzymes from chick-embryo tendon, cartilage and kidneys. These results do not support the hypothesis that lysyl hydroxylase has collagen-type-specific or tissue-specific isoenzymes with markedly different specific activities or immunological properties. The antibodies to chick-embryo lysyl hydroxylase showed a considerable degree of species specificity when examined either by activity-inhibition assay or by double immuno-diffusion. Nevertheless, a distinct, although weak, cross-reactivity was found between the chick-embryo enzyme and those from all mammalian tissues tested. The antiserum showed no cross-reactivity against prolyl 3-hydroxylase, hydroxylysyl galactosyl-transferase or galactosylhydroxylysyl glucosyltransferase in activity-inhibition assays, whereas a distinct cross-reactivity was found against prolyl 4-hydroxylase. Furthermore, antiserum to pure prolyl 4-hydroxylase inhibited lysyl hydroxylase activity. These findings suggest that there are structural similarities between these two enzymes, possibly close to or at their active sites.