Translation of poly-A RNA from rat liver in vitro. Evidence for a high molecular weight subunit of tyrosine aminotransferase

Poly-A RNA extracted from the rat liver was translated in a cell-free wheat germ system and a rabbit reticulocyte lysate. The subunit of tryptophan pyrrolase precipitated by specific antiserum after synthesis in vitro has the same molecular weight as the corresponding subunit derived from the rat liver. With specific antiserum prepared against tyrosine aminotransferase, however, a radioactive protein from both the in vitro assays was precipitated with an about 5% higher molecular weight than the tyrosine aminotransferase subunit precipitated from rat liver. The immunological evidence and the comparison of the specific peptide patterns prepared by cyanogen bromide treatment showed that the in vitro product corresponds to tyrosine aminotransferase. Various concentrations of potassium or spermidine used in the wheat germ translation system did not alter the size of the enzyme subunit synthesized. The run of the tyrosine aminotransferase purified form the rat liver in the SDS-polyacrylamide gel electrophoresis was not influenced by treatment with Escherichia coli alkaline phosphatase. The possibility is discussed that the larger enzyme synthesized in vitro represents a precursor molecule which is cleaved proteolytically in vivo.     

Nonidentity of liver alcohol dehydrogenase and the principal protein target of hepatic azocarcinogen

During hepatocarcinogenesis in the rat by the aminoazo dyes, a principal carcinogen-protein conjugate (azoprotein) is formed in liver cytosol from a normal target protein, whose identity and function are unknown. Based on similarities of amino acid compositions, molecular weights, and subunit sizes of azoprotein and liver alcohol dehydrogenases, others have proposed that liver alcohol dehydrogenase is the principal normal target protein of azocarcinogens during liver carcinogenesis in the rat.In the present study, specific antiserum precipitated the principal liver azoprotein and target protein, but failed to precipitate rat liver alcohol dehydrogenase. The ability of the antiserum to distinguish and to separate the azoprotein and target protein from alcohol dehydrogenase shows that this enzyme is not the principal target protein of the azocarcinogens.     

Immunological distinction between calmodulin-sensitive and calmodulin-insensitive adenylate cyclases

Previous studies using calmodulin-Sepharose affinity chromatography have suggested that bovine brain may contain a mixture of calmodulin-sensitive and -insensitive adenylate cyclase activities (Wescott, K. R., La Porte, D. C., and Storm, D. R. (1979) Proc. Natl. Acad. Sci. U.S.A. 82, 3086-3090). In this study, mice were immunized with a purified preparation of the calmodulin-sensitive adenylate cyclase from bovine brain, and a polyclonal antiserum was obtained which was specific to the calmodulin-sensitive form of the enzyme. The antiserum was not inhibitory and precipitated enzyme activity from a homogeneous preparation of the calmodulin-sensitive adenylate cyclase catalytic subunit. Furthermore, the antiserum did not interact with calmodulin-insensitive adenylate cyclase which was resolved from the calmodulin-sensitive form of the enzyme by calmodulin-Sepharose affinity chromatography. Since the only polypeptide specifically precipitated by the antiserum had an Mr of 135,000, which was identical to the Mr of the catalytic subunit of the enzyme, it is concluded that the antiserum interacted directly and specifically with the catalytic subunit of the calmodulin-sensitive isozyme of adenylate cyclase. Detergent-solubilized membranes from several rat tissues were examined for the presence of calmodulin-sensitive adenylate cyclase using anti-calmodulin-sensitive adenylate cyclase antiserum. Approximately 40-60% of the total adenylate cyclase activity of rat brain and kidney were immunoprecipitated by the antiserum, whereas liver and testes contained no detectable calmodulin-sensitive adenylate cyclase. Approximately 15% of the total adenylate cyclase activity in rat heart and lung was the calmodulin-sensitive form. These data indicate that the calmodulin-sensitive and insensitive adenylate cyclases from bovine brain are immunologically distinct and support the proposal that there may be two or more distinct adenylate cyclase isozymes in brain.     

Immunological characterization of the mitochondrial 2-oxoglutarate carrier from liver and heart. Organ specificity

Antibodies have been prepared against the 2-oxoglutarate transport proteins purified from bovine heart and rat liver mitochondria. The anti-heart antiserum cross-reacts with the 2-oxoglutarate carrier (OGC) from beef, pig, rat and rabbit heart, but not with the OGC from liver of the same animals. Conversely, the anti-liver antiserum recognizes the carrier protein from liver of all species tested but not from heart. Immunoinactivation of oxoglutarate transport activity by the antibodies is also tissue specific. Peptide maps of purified OGC show structural differences between the carrier from heart and liver of the same animal species. These results indicate the existence of isoforms of the OGC in heart and liver.     

Detection of a serum class I molecule in rat with anti-rat liver beta-2-microglobulin

Rat serum was fractionated on a column of Sephacryl-300 and tested with a rabbit anti-rat beta-2-microglobulin (B2m) antiserum. This antiserum was directed against B2m purified from rat liver, and its specificity was confirmed by immunoprecipitation procedures. The antiserum recognized three peaks in the fractionated rat serum: a 200- to 300-kd (kilodalton) fraction, a 40- to 70-kd component, and the free 12-kd B2m. Indirect immunoprecipitation from the 200- to 300-kd fraction led to the identification of a 43-kd polypeptide associated with B2m. A xenoantiserum against RT1 class I antigen also precipitated a similar polypeptide from the same fraction, but this molecule differed in size and antigenic specificity from the one precipitated by anti-rat B2m.This work was supported in part by Grant 59010101 from the Ministry of Education, Science, and Culture, Japan.     

Subunit composition of rat liver glutathione S-transferases

The plasmid pGTR112 contains partial coding sequences for one of the rat liver glutathione S-transferase subunits. We have used immobilized pGTR112 DNA to select for complementary and homologous liver poly(A)-RNAs under conditions of increasing stringency for hybridization. Each fraction of selected poly(A)-RNAs was assayed by in vitro translation followed by immunoprecipitation. A total of four distinct polypeptides precipitated by antiserum against rat liver glutathione S-transferases were resolved by NaDodSO₄ polyacrylamide gel electrophoresis. They are separated into two pairs according to the sequence homology of their poly(A)-RNAs with the pGTR112 DNA. Purified rat liver glutathione S-transferases can be resolved on gradient NaDodSO₄ polyacrylamide gels into four polypeptides. There should be ten isozymes of different binary combinations from four distinct subunits for the rat liver glutathione S-transferases.     

Reversible ATP-induced inactivation of branched-chain 2-oxo acid dehydrogenase.

1. Antiserum was raised against purified Wistar-rat liver UDP-glucuronyltransferase. 2. UDP-glucuronyltransferase activities towards 4-nitrophenol, bilirubin, 1-naphthol and morphine were co-immunoprecipitated from solubilized Wistar-rat liver preparations. 3. UDP-glucuronyltransferase activities towards 1-naphthol, 2-aminophenol and 4-nitrophenol were precipitated from solubilized Gunn-rat liver preparations by this antiserum. 4. UDP-glucuronyltransferase activities towards 1-naphthol, 4-nitrophenol and bilirubin, from Wistar-rat liver, were slightly inhibited by antiserum, whereas 1-naphthol UDP-glucuronyltransferase activity from Gunn-rat livers was greatly inhibited. 5. Measurable Wistar-rat liver glucuronyltransferase activities in washed immunoprecipitates indicate that the enzyme(s) were not merely inhibited by antiserum. 6. Immunoglobulin G purified from this antiserum immunoprecipitated transferase activities towards 4-nitrophenol, bilirubin and 1-naphthol. 7. The washed immunoprecipitates from both rat strains, containing UDP-glucuronyltransferase activity, appear to be similar when analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. 8. Radial-immunodiffusion studies suggest that a smaller amount of UDP-glucuronyltransferase protein is present in Gunn-rat liver than in Wistar-rat liver. 9. The significance of these results in relation to the genetic deficiency in the Gunn rat is discussed.     

Tissue-specificity overrides species-specificity in cytoplasmic cytochrome c oxidase polypeptides

With a high-resolving dodecyl sulfate electrophoretic system rat liver cytochrome c oxidase was separated into 13 different polypeptides. An antiserum against rat liver holocytochrome c oxidase immunoreacted with all 13 polypeptides, as demonstrated by immunofluorescence after transfer of the separated Coomassie blue-stained bands on nitrocellulose and coupling with FITC-protein A ("western blot"). Polypeptide-specific antisera reacted only with their corresponding polypeptides indicating that the various protein bands are represented by individual polypeptides. From total proteins of rat liver, kidney, heart, spleen and skeletal muscle mitochondria, only the cytochrome c oxidase polypeptides showed immunofluorescence with an antiserum against the rat liver holoenzyme. In contrast to the polypeptide from liver, polypeptide VIa from heart and skeletal muscle showed little or no reactivity, indicating a tissue-specificity of this polypeptide. Mitochondrial proteins from pig, bovine and blackbird heart were incubated with an antiserum against the rat liver holoenzyme. Immunoreaction was found with most cytochrome c oxidase polypeptides but not with polypeptide VIa. This result demonstrates less immunological relationship between tissue-specific polypeptides (VIa, VIIa and VIII) of the same species than between tissue-unspecific polypeptides of different species.     

Immunological and sequence interrelationships between multiple human liver and rat glutathione S-transferases

The 13 forms of human liver glutathione S-transferases (GST) (Vander Jagt, D. L., Hunsaker, L. A., Garcia, K. B., and Royer, R. E. (1985) J. Biol. Chem. 260, 11603-11610) are composed of subunits in two electrophoretic mobility groups: Mr = 26,000 (Ha) and Mr = 27,500 (Hb). Preparations purified from the S-hexyl GSH-linked Sepharose 4B affinity column revealed three additional peptides at Mr = 30,800, Mr = 31,200, and Mr = 32,200. Immunoprecipitation of human liver poly(A) RNAs in vitro translation products revealed three classes of GST subunits and related peptides at Mr = 26,000, Mr = 27,500, and Mr = 31,000. The Mr = 26,000 species (Ha) can be precipitated with antisera against a variety of rat liver GSTs containing Ya, Yb, and Yc subunits, whereas the Mr = 27,500 species (Hb) can be immunoprecipitated most efficiently by antiserum against the anionic isozymes as well as a second Yb-containing isozyme (peak V) from the rat liver. The Mr = 31,000 band can be immunoprecipitated by antisera preparations against sheep liver, rat liver, and rat testis isozymes. Human liver GSTs do not have any subunits of the rat liver Yc mobility. Antiserum against the human liver GSTs did not cross-react with the Yc subunits of rat livers or brains in immunoblotting experiments. The human liver GST cDNA clone, pGTH1, selected human liver poly(A) RNAs for the Ha subunit(s) in the hybrid-selected in vitro translation experiments. Southern blot hybridization results revealed cross-hybridization of pGTH1 with the Ya, Yb, and Yc subunit cDNA clones of rat liver GSTs. This sequence homology was substantiated further in that immobilized pGTH1 DNA selected rat liver poly(A) RNAs for the Ya, Yb, and Yc subunits with different efficiency as assayed by in vitro translation and immunoprecipitation. Therefore, we have demonstrated convincingly that sequence homology as well as immunological cross-reactivity exist between GST subunits from several rat tissues and the human liver. Also, the multiple forms of human liver GSTs are most likely encoded by a minimum of three different classes of mRNAs. These results suggest a genetic basis for the subunit heterogeneity of human liver GSTs.     

Demonstration of cross-reacting material in Tay–Sachs disease

Antibodies against placental hexosaminidase A and kidney alpha-subunits were raised in rabbits after cross-linking the antigens with glutaraldehyde. Anti-(alpha(n)-subunit) antiserum (anti-alpha(n)) precipitated hexosaminidase A but not hexosaminidase B, whereas anti-(hexosaminidase A) antiserum precipitated both hexosaminidases A and B. Specific anti-(hexosaminidase A) antiserum was prepared by absorbing antiserum with hexosaminidase B. Both anti-alpha(n) and anti-(hexosaminidase A) antisera precipitated the CR (cross-reacting) material from eight unrelated patients with Tay-Sachs disease. Immunotitration, immunoelectrophoresis, double-immunodiffusion and radial-immunodiffusion techniques were used to demonstrate the presence of CR material. The CR-material-antibody complex was enzymically inactive. Antiserum raised against kidney or placental hexosaminidase A, without cross-linking with glutaraldehyde, failed to precipitate the CR material, implying that treatment of the protein with glutaraldehyde exposes antigenic determinants that are hidden in the native protein. Since anti-(hexosaminidase B) antiserum did not precipitate the CR material during the immunoelectrophoresis of Tay-Sachs liver extracts, it is suggested that altered alpha-subunits do not combine with beta-subunits. By using immunotitration we have demonstrated the competition between the hexosaminidase B-free Tay-Sachs liver extract and hexosaminidase A for the common binding sites on monospecific anti-(cross-linked hexosaminidase A) antiserum. The amount of CR material in the liver samples from seven cases of Tay-Sachs desease was found to be in the same range as theoretically calculated alpha-subunits in normal liver samples. Similar results were obtained by the radial-immunodiffusion studies. The present studies therefore suggest that Tay-Sachs disease is caused by a structural-gene mutation.     

Purification of mRNA coding for the enzyme deficient in hereditary tyrosinemia, fumarylacetoacetate hydrolase

As a step towards the cloning of the gene for fumarylacetoacetate hydrolase (FAH), we have purified the FAH mRNA from rat liver by specific immunoadsorption of polysomes. The relative abundance of this mRNA has been estimated to be 0.14%. The major in vitro translation product of the purified mRNA preparation is specifically precipitated by a rabbit anti-rat FAH antiserum and it is, furthermore, undistinguishable by criteria of mass and charge from purified rat FAH.     

Anti-catechol-O-methyltransferase: Demonstration of specificity and immunological cross-reactivity with the enzyme from rat liver,kidney, brain,and choroid plexuses

An antiserum to rat liver catechol-O-methyltransferase (COMT) was utilized in the immunological characterization of COMT from rat kidney, brain, and choroid plexuses, in addition to rat liver. The presence of anti-COMT activity was confirmed by the direct inhibition of the activity of the enzyme from rat liver by small quantities of the antiserum and by the inhibition of the activity of the enzyme from rat brain. The specificity of the antiserum was demonstrated both by immunoelectrophoresis of rat liver COMT, and by a partial purification of rat liver COMT in which changes in COMT specific activity were correlated with the appearance of a precipitin line in double-immunodiffusion experiments. The antigenic similarity of the enzyme derived from rat liver, kidney, brain, and choroid plexuses was demonstrated by the formation of a precipitin line of identity when preparations from these four tissues were diffused against the antiserum.     

Translation in vivo and in vitro of proteins resembling apoproteins of rat plasma very low density lipoprotein.

Antibodies raised against rat plasma apoVLDL and a purified fraction of arginine-rich peptides (ARP) were labeled with Na125I and were shown to bind to polyribosomes isolated from rat liver. Antibody fractions enriched by selective affinity chromatography exhibited increased levels of binding to polysomes. Anti-apoVLDL immunoreactivity was further resolved into anti-ARP and anti apoB components, each reactive with a distinct polysome population. Binding was specific for rat polysomes, and was directed toward nascent polypeptide chains. About 2% of normal rat liver polysomes were recovered by indirect immunoprecipitation with anti-apoVLDL. Ribonucleic acid (RNA) extracted from this immunoprecipitate contained species with polyadenylate (poly[A] sequences characteristic of eukaryotic messenger RNA (mRNA). These species, purified by affinity chromatography on poly(U)-Sepharose, stimulated the in vitro synthesis of immunoprecipitable apoVLDL-like proteins by about 17-fold when compared to unfractionated rat liver mRNA. Most of the in vitro translation products precipitated by purified anti-ARP migrated identically on polyacrylamide gel electrophoresis with unlabeled purified ARP. Some implications of these findings with respect to plasma VLDL biosynthesis are discussed.     

Taurine Biosynthesis in Rat Brain: A New Specific and Sensitive Microassay of Cysteine Sulfinate Decarboxylase (CSDI) Activity Through Selective Immunotrapping and Its Use for Distribution Studies

Cysteine sulfinate decarboxylase (CSD), the putative biosynthetic enzyme for taurine, has been shown to exist in two forms in rat brain, respectively CSDI and CSDII, one of which (CSDII) is considered to be in fact glutamate decarboxylase (GAD). CSDI assay after immunotrapping was made possible by using an anti-CSD antiserum raised in sheep immunized with a partially purified CSD fraction from liver. This antiserum immunoprecipitated both liver CSD and brain CSDI activities with the same affinity but did not inhibit their enzymatic activities. The immunotrapping of CSDI was selective without any contamination by GAD/CSDII activity. The immunotrapped CSD activity, which corresponded exactly to the amount of CSD not precipitated by a GAD/CSDII antiserum, was not inhibited by a specific irreversible GAD inhibitor. A quantitative, selective and sensitive assay was thus developed by measuring CSD activity on the solid phase after immunotrapping. Kinetic parameters of the immunotrapped enzyme remained unchanged. CSDI activity represented only a fraction, around 20% with saturating concentration of substrate, of the total CSD activity in rat brain homogenate. This indicates that most studies on total CSD activity dealt essentially with CSDII activity that is indeed GAD. Regional and subcellular distributions of CSDI have been determined. CSDI activity was about threefold higher in the richest (cerebellum) compared to the poorest (striatum) region without any correlation with GAD/CSDII distribution. Subcellular distribution showed a fourfold enrichment of CSDI activity in the synaptosomal fraction. The precise role of CSDI and CSDII in the biosynthesis of taurine in vivo remains to be elucidated.     

Effects of dithiothreitol and thioredoxines on the in vitro activity of enzymes of the urea cycle in rats

The five urea cycle enzymes were studied in desactivated extracts of rat liver. After reduction by dithiothreitol (DTT) and in presence of Mg2+ ions, thioredoxines isolated from rat liver were able to activate carbamyl phosphate synthetase-I (CPS-I) and argininosuccinate synthetase (ASS) respectively by 468% and by 370%. Thioredoxines were purified from adult rat liver and an antiserum was raised to these proteins. After immunologic quantitation, their level in adult rat was 0.103 mg/g liver.     

Precipitation of polyribosomes with pepsin digested antibodies

Polyribosomes prepared from rabbit reticulocytes were precipitated with a “γG” fraction prepared from goat antiserum to rabbit hemoglobin (specific). A similar preparation from rabbit antiserum to rat hemoglobin (control) precipitated the same proportion of the polyribosomes. The non-specificity of the precipitation was significantly reduced by pre-digestion of the antibodies with pepsin. After pre-digestion of either whole antiserum or of the “γG” fraction, the precipitation of polyribosomes by the specific antibodies was increased slightly while precipitation of polyribosomes by the control antibodies was virtually eliminated.     

A chloride- and calcium-dependent glutamate-binding protein from rat brain. Identification as a ubiquitous constituent of the inner mitochondrial membrane

We have recently solubilized and enriched a chloride- and calcium-dependent glutamate-binding protein from rat brain (Brose, N., Halpain, S., Suchanek, C., and Jahn, R. (1989) J. Biol. Chem. 264, 9619-9625). The partially purified protein fraction, containing two major protein components of 51,000 Da and 105,000 Da, was used to generate a rabbit antiserum. This serum quantitatively precipitated the binding activity from membrane extracts. Small amounts of the antiserum inhibited glutamate binding when chloride was absent from the incubation medium. Three protein bands were labeled by the serum on immunoblots. From the affinity purified antibody fractions contained in the serum, only the antibodies directed against a 51,000-Da protein were able to immunoprecipitate the binding activity, indicating that this protein is an essential component of the binding site. A survey of a variety of rat tissues by immunoblot analysis revealed a ubiquitous distribution of the protein. After subcellular fractionation of liver and brain, the 51,000-Da protein copurified with mitochondrial markers. Furthermore, exclusive labeling of mitochondria was observed by light and electron microscopy immunocytochemistry. Subfractionation of purified liver mitochondria resulted in a selective association of the protein with inner mitochondrial membranes. Pharmacological characterization of glutamate binding to liver mitochondrial membranes revealed a pattern almost identical to that of the chloride- and calcium-dependent glutamate-binding site in rat brain.     

Characteristic distribution of cathepsin E which immunologically cross-reacts with the 86-kDa acid proteinase from rat gastric mucosa

The antiserum raised against the high-molecular-weight acid proteinase from rat gastric mucosa, termed 86-kDa acid proteinase, has been shown to recognize rat cathepsin E, but not cathepsin D (Muto, N. et al. (1987) J. Biochem. 101, 1069-1075). Using this specific antiserum, characteristic distribution of cathepsin E in rats was demonstrated. The enzyme was detected in a limited number of tissues, such as stomach, thymus, spleen, bladder, and erythrocyte membranes. Among them, the highest activity was observed in the stomach. In contrast, cathepsin D immunoreactive with the antiserum specific to rat gastric cathepsin D was demonstrated in all the tissues examined. Cathepsin E-type enzymes partially purified from these five tissues were precipitated in the same manner by the specific antiserum, and they had the same molecular weight, electrophoretic mobility, and resistance against denaturation by 4 M urea. These results indicate that they could be exactly classified as cathepsin E. This type of enzyme was also detectable in mice and guinea pigs, but they showed relatively weak immunoreactivities with the antiserum. Thus, it is concluded that the distribution of cathepsin E is intrinsically different from ordinary cathepsin D, suggesting that it has a different physiological role from cathepsin D.     

Localization of immunoreactive regions in the beef heart adenine nucleotide carrier using rabbit antisera against the carboxyatractyloside-liganded and the sodium dodecyl sulfate denaturated carrier forms

The existence of different antigenic determinants in the beef heart adenine nucleotide (AdN) carrier was demonstrated by exploring the reactivity of fragments of the carrier protein with rabbit antisera directed against either the beef heart AdN carrier denatured with sodium dodecyl sulfate (NaDodSO4 carrier) or the beef AdN carrier liganded by the specific inhibitor carboxyatractyloside (CATR-carrier). The antigenic determinants reacting with antiserum to the CATR-carrier appeared to be close to the N- and C-terminal ends of the carrier protein, whereas those reacting with antiserum to the NaDodSO4 carrier were located preferentially in the central region of the protein. The same antisera were used to study the immunogenic specificity of the beef liver AdN carrier, the rat heart AdN carrier, and the rat liver AdN carrier. The beef liver and rat heart AdN carriers were found to react with both antisera whereas the rat liver AdN carrier reacted essentially with the CATR-carrier antiserum.     

Monoclonal Antibodies and Polyvalent Antiserum to Chicken Choline Acetyltransferase

Monoclonal antibodies (mAbs) to chick choline acetyltransferase (ChAT) were obtained from mouse-hybridoma cultures after immunization with partially purified enzyme isolated from optic lobes. Antibodies that bound active enzyme were detected in 11 hybridoma cultures. The mAbs showed cross-reactivity to ChAT from quail and beef but not to ChAT from several other species. An affinity column prepared with one of the mAbs was used to purify ChAT to apparent homogeneity. Polyclonal antiserum to mAb affinity-purified ChAT was produced in a rabbit. This antiserum inhibited chick ChAT activity and quantitatively precipitated ChAT activity from solution. On immunoblots, the antiserum stained ChAT and two other proteins. After preadsorption of the antiserum with effluent from the mAb affinity column, the antiserum became monospecific for ChAT. This antiserum was useful for immunocytochemical localization of ChAT, it selectively stained neuronal cell bodies in chick spinal cord and rat brain at locations known to contain cholinergic neurons.