Purification and cDNA cloning of Xenopus laevis skin peptidylhydroxyglycine N-C lyase, catalyzing the second reaction of C-terminal alpha-amidation

The alpha-amidation of glycine-extended peptides is a two-step reaction catalyzed by peptidylglycine alpha-hydroxylating monooxygenase (PHM) and peptidylhydroxyglycine N-C lyase (PHL). PHL was purified to homogeneity from Xenopus laevis skin and its partial amino acid sequence (including the N-terminal 35 residues) was determined. It was found that the cDNA codes for a 935-residue precursor protein (AE-III protein), containing the PHM and PHL sequences at its N terminus and C terminus, respectively. The PHM sequence in AE-III protein is completely identical to that deduced from the nucleotide sequence of X. laevis AE-I cDNA, which encodes only PHM, except that the AE-I protein has an extra 10 residues at its C terminus. It is suggested that AE-I and AE-III mRNA are encoded by the same gene and produced by alternative splicing.

The C-S lyases of higher plants: homogeneous beta-cystathionase of spinach leaves

S-Substituted cysteines and their derivatives are prominent secondary amino acids in a number of plant families. The substituents are often specific and unique to each family. Cystathionine, however, is an ubiquitous S-substituted cysteine found in all autotrophic plants since it is an intermediate in the biosynthesis of methionine. beta-Cystathionase will produce homocysteine and pyruvate from cystathionine by a beta-elimination reaction. The present report describes the purification of this enzyme to homogeneity from spinach leaves and some of its properties. The enzyme has a molecular weight of 210,000 and consists of four identical subunits of Mr 53,000. It has a pH optimum for activity of 8.6-8.7 and utilizes pyridoxal-5'-phosphate as a cofactor. Its specificity is limited to L-cystathionine, L-djenkolate, and L-cystine as substrates with a relative activity of 100:126:17, respectively. It is not a glycoprotein unlike a number of previously described plant C-S lyases.

Purification and properties of an ethylene-forming enzyme from Pseudomonas syringae pv. phaseolicola PK2

A novel ethylene-forming enzyme that catalyses the formation of ethylene from 2-oxoglutarate was purified from a cell-free extract of Pseudomonas syringae pv. phaseolicola PK2. It was purified about 2800-fold with an overall yield of 53% to a single band of protein after SDS-PAGE. The purified enzyme had a specific activity of 660 nmol ethylene min-1 (mg protein)-1. The molecular mass of the enzyme was approximately 36 kDa by gel filtration and 42 kDa by SDS-PAGE. The isoelectric point and optimum pH were 5.9 and ca. 7.0-7.5, respectively. There was no homology between the N-terminal amino acid sequence of the ethylene-forming enzyme of Ps. syringae pv. phaseolicola PK2 and the sequence of the ethylene-forming enzyme of the fungus Penicillium digitatum IFO 9372. However, the two enzymes have the following properties in common. The presence of 2-oxoglutarate, L-arginine, Fe2+ and oxygen is essential for the enzymic reaction. The enzymes are highly specific for 2-oxoglutarate as substrate and L-arginine as cofactor. EDTA, Tiron, DTNB [5,5'-dithio-bis(2-nitrobenzoate)] and hydrogen peroxide are all effective inhibitors.

Purification and some properties of the squalene-tetrahymanol cyclase from Tetrahymena thermophila

The membrane-bound enzyme from Tetrahymena thermophila responsible for the conversion of squalene into the quasi-hopanoid tetrahymanol was purified 297-fold to near homogeneity. Purification involved solubilization by octylthioglucoside, chromatography on DEAE-trisacryl, hydroxyapatite and FPLC ion-exchange on Mono Q. The apparent KM was found to be 18 microM. 2,3-Iminosqualene and N,N-dimethyldodecylamine-N-oxide are effective inhibitors of the cyclase with I50 values of 50 and 30 nM, respectively. The cyclase has a molecular mass of 72 kDa as judged by electrophoresis in polyacrylamide gels under denaturating conditions. The optimal enzymatic activity was obtained at pH 7.0 and 30 degrees C. The solubilized enzyme needs the presence of detergent for maintaining activity. The influence of different detergents on cyclase activity was studied. Triton X-100 proved to be a strong inactivator of the enzyme. Solubilization of the cyclase in Tween 80 and digitonin inactivates the enzyme. However, its activity can be recovered by complementation of the assay buffer with octylthioglucoside above its critical micellar concentration. We suggest that this approach might be applicable to other membrane-bound proteins.

Purification and characterization of a novel lyase from Cellulomonas sp. that degrades Fusarium and Gibberella acidic polysaccharides

A Cellulomonas sp. isolated from soil produced a novel lyase that degraded the acidic polysaccharide of Fusarium sp. M7-1 with the formation of mannose and O-beta-D-mannopyranosyl-(1----2)-D-mannose. DEAE-Toyopearl 650M column chromatography showed three lyase activity peaks (fractions I, II, and III). The major fraction was purified to homogeneity by polyacrylamide gel electrophoresis analysis, and its molecular weight was 74,000. The optimum pH was 6.5 to 8.0 and the stable pH range was 6.0 to 8.0. The purified enzyme did not degrade glucuronic or galacturonic acid-containing polysaccharides such as chondroitin, hyaluronic acid, pectin, or pectic acid. However, the purified enzyme specifically degraded various Fusarium and Gibberella acidic polysaccharides, and unsaturated sugars were produced with the release of mannose and O-beta-D-mannopyranosyl-(1----2)-D-mannose. These results suggest that the acidic polysaccharides derived from Fusarium and Gibberella have similar structures.

Ureidoglycolate amidohydrolase from developing French bean fruits (Phaseolus vulgaris [L.].)

Ureidoglycolate is an intermediate of allantoin catabolism in ureide-transporting legumes. This report describes the first purification of ureidoglycolate degrading activity (UGDA) from plant tissue in which the enzyme has been separated from urease. The enzyme from developing fruits of Phaseolus vulgaris has been purified 48-fold to give a preparation free of allantoinase and urease activity. UGDA was inhibited by EDTA while the Vmax was increased in the presence of Mn2+. The Km values for ureidoglycolate in the presence and the absence of Mn2+ were 2.0 and 5.4 mM, respectively. In the absence of Mn2+ UGDA was heat labile at 40 degrees C, but in the presence of Mn2+ the activity was stable up to temperatures of 60 degrees C. The Mr of UGDA was determined to be 300,000 by gel filtration chromatography and the pH optimum ranged from pH 7.0 to 8.5. Ammonia was determined to be the nitrogen-containing product of UGDA by a microdiffusion assay. This enzyme should therefore be described as ureidoglycolate amidohydrolase. The activity was shown to be associated with peroxisomes by fractionation of a crude extract on a sucrose density gradient. The products of ureidoglycolate degradation are glyoxylate, ammonia, and presumably carbon dioxide, which can be readily utilized by pathways of metabolism that are known to be present in this organelle.

Purification and characterization of haloalcohol dehalogenase from Arthrobacter sp. strain AD2

An enzyme capable of dehalogenating vicinal haloalcohols to their corresponding epoxides was purified from the 3-chloro-1,2-propanediol-utilizing bacterium Arthrobacter sp. strain AD2. The inducible haloalcohol dehalogenase converted 1,3-dichloro-2-propanol, 3-chloro-1,2-propanediol, 1-chloro-2-propanol, and their brominated analogs, 2-bromoethanol, as well as chloroacetone and 1,3-dichloroacetone. The enzyme possessed no activity for epichlorohydrin (3-chloro-1,2-epoxypropane) or 2,3-dichloro-1-propanol. The dehalogenase had a broad pH optimum at about 8.5 and a temperature optimum of 50 degrees C. The enzyme followed Michaelis-Menten kinetics, and the Km values for 1,3-dichloro-2-propanol and 3-chloro-1,2-propanediol were 8.5 and 48 mM, respectively. Chloroacetic acid was a competitive inhibitor, with a Ki of 0.50 mM. A subunit molecular mass of 29 kDa was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. With gel filtration, a molecular mass of 69 kDa was found, indicating that the native protein is a dimer. The amino acid composition and N-terminal amino acid sequence are given.

Purification of chorismate synthase from a cell culture of the higher plant Corydalis sempervirens Pers

Chorismate synthase (EC 4.6.1.4) was purified from a cell suspension culture of Corydalis sempervirens almost 1000-fold to near homogeneity. The subunit Mr estimated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate was 41,900. The Mr of the native enzyme was estimated to be 80,100 by gel filtration, suggesting a dimeric structure. Antisera directed against the 41.9-kDa protein also reacted with the native enzyme. Further confirmation of the identity of the purified protein was obtained by sequence comparison of a tryptic peptide with known sequences of the Escherichia coli and Neurospora crassa chorismate synthases.

Biosynthesis of cyclic 2,3-diphosphoglycerate. Isolation and characterization of 2-phosphoglycerate kinase and cyclic 2,3-diphosphoglycerate synthetase from Methanothermus fervidus

Starting from 2-phosphoglycerate the biosynthesis of cDPG comprises two steps: (i) the phosphorylation of 2-phosphoglycerate to 2,3-diphosphoglycerate and (ii) the intramolecular cyclization to cyclic 2,3-diphosphoglycerate. The involved enzymes, 2-phosphoglycerate kinase and cyclic 2,3-diphosphoglycerate synthetase, were purified form Methanothermus fervidus. Their molecular and catalytic properties were characterized.

Thermostable S-alkylcysteine alpha, beta-lyase from a thermophile: purification and properties

S-Alkylcysteine alpha, beta-lyase was found in a thermophile, Bacillus sp. 41A, which was newly isolated from soil, and purified to homogeneity from the cell extract. The enzyme has a molecular weight of about 76,000, and is composed of two subunits identical in molecular weight (39,000). The enzyme requires pyridoxal 5'-phosphate as a coenzyme, and catalyzes alpha, beta-elimination of S-methyl-L-cysteine and its analogs such as S-ethyl-L-cysteine, L-djenkolate, L-cystine, Se-methyl-L-selenocysteine, and O-methyl-DL-serine. However, S-methyl-D-cysteine, D-cystine, L-methionine, and L-norleucine were inert. The enzyme also catalyzes the beta-replacement reaction of S-methyl-L-cysteine with various thiols to yield the corresponding S-substituted cysteines. In addition to S-methyl-L-cysteine, Se-methyl-L-selenocysteine and O-methyl-DL-serine also serve as beta-substituent acceptors in the beta-replacement reaction. The enzyme is most active at 70 degrees C and stable at high temperatures. Automated Edman degradation provided the N-terminal sequence of the first 44 amino acids. The amino acid sequence in the vicinity of the lysyl residue to which pyridoxal 5'-phosphate is bound, was -Lys-His-Gln-Arg- by Edman degradation of the pyridoxyl peptide obtained by digestion with trypsin after reduction with sodium borohydride.

Purification and characterization of S-alkylcysteine alpha,beta-lyase from Pseudomonas putida

S-Alkylcysteine alpha,beta-lyase [EC 4.4.1.6] was purified to more than 90% homogeneity from the cell extract of Pseudomonas putida ICR 3640. The enzyme has a molecular weight of about 195,000, and is composed of six subunits identical in molecular weight (37,000). Pyridoxal 5'-phosphate is required as a cofactor. The enzyme catalyzes the alpha,beta-elimination of S-methyl-L-cysteine and its analogs such as S-ethyl-L-cysteine, L-djenkolate, Se-methyl-DL-selenocysteine, and O-methyl-L-serine. However, S-methyl-D-cysteine, L-methionine, and L-norvaline were inert. The enzyme catalyzes also the beta-replacement reaction of the thiomethyl group of S-methyl-L-cysteine with various thiols to yield the corresponding S-substituted cysteines. In addition to S-methyl-L-cysteine, Se-methyl-DL-selenocysteine and O-methyl-L-serine also serve as substrates in the beta-replacement reaction.

Cloning and sequence of two different cDNAs encoding 1-aminocyclopropane-1-carboxylate synthase in tomato

1-Aminocyclopropane-1-carboxylate synthase (ACC synthase; S-adenosyl-L-methionine methylthioadenosine-lyase, EC 4.4.1.14), the key enzyme in ethylene biosynthesis, was purified 5000-fold from induced tomato pericarp. ACC synthase activity was unambiguously correlated with a 45-kDa protein by two independent methods. Peptide sequences were obtained both from the N terminus after electroblotting and from tryptic peptides separated by reversed-phase chromatography. Mixed oligonucleotide probes were used to screen a lambda gt11 library prepared from RNA of induced pericarp tissue. Putative ACC synthase clones were isolated with a frequency of 0.01%. One of these contained a 1.9-kilobase insert with a single open reading frame encoding a polypeptide of 55 kDa. A second, partial cDNA clone was found that differed from the first one in 18% of its bases. Genomic Southern blotting suggests possible tandem organization of the two genes in tomato. The entire coding region was expressed in Escherichia coli and the denatured recombinant polypeptide was used to raise polyclonal antibodies. The antibody preparation both immunoinhibits and immunoprecipitates ACC synthase activity from an enriched tomato extract, confirming the identity of the clone. Northern blot analysis demonstrates that the ACC synthase messenger accumulation is coordinated with fruit ripening.

DNA photoreactivating enzyme from the cyanobacterium Anacystis nidulans

Photoreactivating enzyme, which specifically monomerizes pyrimidine dimers in UV-irradiated DNA, was purified 21,000-fold from the cyanobacterium Anacystis nidulans to apparent homogeneity with 41% overall yield. The enzyme consists of a single protein chain with 53,000 molecular weight. Maximal activity was found at pH 6.2 and 0.1 M NaCl. Purified photoreactivating enzyme exhibits a marked absorption spectrum with a main band in the blue region (maximum 437 nm), a protein band (maximum 266 nm), and a low intensity band above 500 nm. The molar extinction coefficient of native enzyme was estimated 53,000 at 437 nm. The action spectrum for photoreactivation shows maximal activity at 440 nm and correlates closely with the 437-nm absorption band. The enzyme contains two different intrinsic chromophores in equimolar amounts, which were identified as 7,8-didemethyl-8-hydroxy-5-deazariboflavin (FO) and (reduced) FAD. The low intensity absorption band of native photoreactivating enzyme exhibits a shoulder at 498 and maxima at 588 and 634 nm. This band is attributed to a neutral FAD semiquinone radical which accounts for the major part of the FAD present in dark equilibrated enzyme. Preillumination at 585 nm bleaches the semiquinone spectrum due to formation of fully reduced FAD, but exposure to air in the dark restores the spectrum completely. On preillumination at 437 nm the disappearance of FAD semiquinone is more rapid, indicating that the photoreduction is sensitized by the 8-hydroxy-5-deazaflavin chromophore. The 8-hydroxy-5-deazaflavin and possibly also the reduced FAD chromophore appear to act as a primary photon acceptor in the photoreactivation process.

Bioactivation mechanism of cytotoxic homocysteine S-conjugates

S-(1,2-Dichlorovinyl)-L-homocysteine is a much more potent nephrotoxin than the corresponding cysteine S-conjugate S-(1,2-dichlorovinyl)-L-cysteine (A. A. Elfarra, L. H. Lash, and M. W. Anders (1986) Proc. Natl. Acad. Sci. USA 83, 2667-2671). The objective of the present experiments was to test the hypothesis that the increased toxicity of homocysteine S-conjugates may be associated with the formation of the reactive metabolite 2-oxo-3-butenoic acid, which may arise via a nonenzymatic retro-Michael elimination reaction from the 2-oxo acid metabolites of homocysteine S-conjugates. S-(2-Benzothiazolyl)-L-homocysteine, which was a substrate for purified bovine kidney cysteine conjugate beta-lyase (glutamine transaminase K) and whose metabolism was dependent on the presence of a 2-oxo acid, was cytotoxic in isolated rat kidney cells and was toxic to rat renal mitochondria, whereas the cysteine S-conjugate S-(2-benzothiazolyl)-L-cysteine had little effect. L-Methionine sulfoximine, L-canavanine, and the Michael acceptor methyl vinyl ketone were cytotoxic. The 2-hydroxy acid analogs of S-(1,2-dichlorovinyl)-L-homocysteine and 2-oxo-3-butenoic acid, S-(1,2-dichlorovinyl)-2-hydroxy-4-mercaptobutanoic acid and 2-hydroxy-3-butenoic acid, respectively, which are expected to be metabolized by rat renal L-2-hydroxy (L-amino) acid oxidase to yield 2-oxo-3-butenoic acid, were also cytotoxic. To obtain evidence for the formation of 2-oxo-3-butenoic acid as a product of the metabolism of L-homocysteine S-conjugates and analogs, trapping experiments were conducted. S-(2-Benzothiazolyl)-L-homocysteine, S-(1,2-dichlorovinyl)-L-homocysteine, L-methionine sulfoximine, and L-canavanine were converted by snake venom L-amino acid oxidase to 2-oxo-3-butenoic acid, which was trapped by the nucleophile methanethiol to yield 4-methylthio-2-oxobutanoic acid; the trapped product was derivatized with 2,4-dinitrophenylhydrazine and was identified by its electronic absorption spectrum and by high-performance liquid chromatography. Similar trapping experiments conducted with kidney homogenates and purified beta-lyase were not successful. The data indicate that the bioactivation of homocysteine S-conjugates and analogs involves the enzymatic formation of the corresponding 2-oxo acids followed by a nonenzymatic retro-Michael elimination reaction to yield the Michael acceptor 2-oxo-3-butenoic acid, which may contribute to the observed cytotoxicity of homocysteine S-conjugates.

Purification and characterization of human kidney cytosolic cysteine conjugate beta-lyase activity

The central role of cysteine conjugate beta-lyase (beta-lyase) in the bioactivation of nephrotoxic halogenated hydrocarbons and the possibility of human exposure to these chemicals has focused interest on the beta-lyase from human kidney. Human kidney tissue was collected as surgical waste material, and subcellular fractions were isolated by differential centrifugation. Human beta-lyase activity, determined with S-(2-benzothiazolyl)-L-cysteine (BTC) as the substrate, was present in the cytosolic, mitochondrial, and microsomal fractions, but was highest in the cytosolic fraction. Activity in human kidney cytosol was about 10% of that present in rat kidney cytosol. Human kidney cytosolic beta-lyase activity, with BTC as the substrate, was not stimulated by pyridoxal phosphate or by exogenous 2-keto acids. Cytosolic beta-lyase activity was purified 280-fold with a yield of 12% from human kidneys unsuitable for transplantation. The beta-lyase activity copurified with cytosolic glutamine transaminase K and exhibited a molecular mass of 85 kDa on a Sephacryl 5300 column and a subunit molecular mass of 45 kDa by gel electrophoresis. Both BTC and its homocysteine analogue S-(2-benzothiazolyl)-L-homocysteine were excellent substrates, exhibiting Km and kcat values of 0.97 mM and 2.78 mM and 9.35 min-1 and 6.90 min-1, respectively. beta-Lyase activity was inhibited by aminooxyacetic acid, indicating that the human cytosolic enzyme contains pyridoxal phosphate, and by the nephrotoxins S-(1,2-dichlorovinyl)-L-cysteine and S-(1,2-dichlorovinyl)-L-homocysteine, which serve as alternative substrates.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the trichodiene synthase gene of Fusarium sporotrichioides in Escherichia coli results in sesquiterpene production

Trichodiene synthase is a sesquiterpene cyclase involved in the biosynthesis of trichothecene mycotoxins. We report that insertion of the unaltered trichodiene synthase gene of Fusarium sporotrichioides into the Escherichia coli expression vector pDR540 produced an inactive polypeptide with a molecular weight approximately 2000 greater than that of trichodiene synthase. This result is consistent with the presence of an intron in the trichodiene synthase gene, and prompted us to specifically delete a putative 60-nucleotide intron sequence. Insertion of the intron-deleted open reading frame into pDR540 resulted in the production of active enzyme. Trichodiene synthase activity in crude extracts from induced cultures was 0.07 nmol/min/mg of protein and represented 0.05-0.10% of the total cell protein. A cross-reactive protein was present with the same apparent molecular weight as the subunit of native trichodiene synthase. The recombinant enzyme was partially purified and shown to have properties closely resembling those of the native enzyme. Trichodiene was detected in ethyl acetate extracts from induced cultures at a concentration of 60 micrograms/liter after 4.5 h. These findings support the primary structure recently reported for trichodiene synthase and demonstrate that the expression of a sesquiterpene cyclase in E. coli results in sesquiterpene production.

Purification and properties of Methanobacterium thermoautotrophicum DNA photolyase

We have purified DNA photolyase from the autotrophic anaerobic archaebacterium Methanobacterium thermoautotrophicum to near homogeneity by a two-column affinity chromatography. The purified enzyme has an Mr = 60,000 and shows near UV absorption peak at 440 nm and a fluorescence emission maximum at 462 nm indicating that it contains 8-hydroxy-5-deazaflavin (coenzyme F420) as an intrinsic chromophore. The photolyase binds with high specificity to thymine dimer in DNA with an equilibrium binding constant, KA = 1.4 x 10(9) M-1, and a dissociation rate constant, koff = 1.4 x 10(-4) s-1 (t1/2 = 43 min). Despite 6-fold higher affinity compared to the folate-containing Escherichia coli photolyase the two enzymes apparently contact the same phosphates around the thymine dimer: the phosphate immediately 5' and the three phosphates immediately 3' to the dimer on the damaged strand and the phosphate across from the dimer in the minor groove on the complementary strand. The absolute action spectrum of the Methanobacterium photolyase in the 400-500-nm region closely matches the absorption of the enzyme-bound F420. The quantum yield (phi) over this region is constant and is approximately 0.2. The value is measurably smaller than the quantum yields reported for other DNA photolyases.

A microbial carbon-phosphorus bond cleavage enzyme requires two protein components for activity

Enterobacter aerogenes IFO 12010 contains a carbon-phosphorus (C-P) bond cleavage enzyme catalyzing the liberation of inorganic phosphate from various alkyl- and phenylphosphonic acids. The enzyme in the bacterium was found to be composed of two physically different protein components, E2 and E3. The molecular weights of E2 and E3 were 560,000 and 110,000, respectively, and E3 was resolved into two apparently homogeneous subunits. Neither component alone could catalyze the C-P bond cleavage reaction, but the reaction was efficiently catalyzed when the components were mixed.

[Isolation, various physico-chemical and catalytic properties of L-methionine-gamma-lyase from Pseudomonas taetrolens]

Homogeneous preparation of L-methionine gamma-lyase was isolated from Ps. taetrolens. As shown by gel filtration and gradient polyacrylamide gel electrophoresis molecular mass of the native L-methionine gamma-lyase was 130-135 kDa. Polyacrylamide gel electrophoresis in presence of 0.1% SDS showed that L-methionine gamma-lyase proved to be a tetramer, which consisted of identical subunits with a molecular mass of 34 kDa. Pyridoxal-5'-phosphate was bound to the enzyme in the ratio of four moles of the cofactor per a mole of protein. The absorption spectrum of the enzyme exhibited maximal values at 420 nm, which is specific for a number of pyridoxal phosphate-containing enzymes. L-methionine gamma-lyase from Ps. taetrolens was found to be dissimilar in its physicochemical and catalytic properties to the same enzymes from other sources.

Purification and partial characterization of 1-aminocyclopropane-1-carboxylate synthase from tomato pericarp

1-Aminocyclopropane-1-carboxylate synthase was purified 5000-fold from LiCl-induced tomato fruit slices by conventional and high-performance liquid chromatography. The final preparation was estimated to be between 25% and 50% pure. Two-dimensional gel electrophoresis indicates that 1-aminocyclopropane-1-carboxylate synthase activity is associated with a 45-kDa polypeptide, with a pI of 5.8 +/- 0.2. The enzyme is inactivated both by its substrate, S-adenosyl-L-methionine (AdoMet) and by one of its products, 1-aminocyclopropane-1-carboxylate. Due to the extremely low abundance of the protein it was necessary to scale up the extraction in order to obtain reasonable amounts for sequence analysis. Therefore, 200 kg tomatoes were extracted on semi-industrial scale and 1-aminocyclopropane-1-carboxylate synthase purified. This yielded approximately 150 micrograms enzyme.

Specificity of S-adenosyl-L-methionine in the inactivation and the labeling of 1-aminocyclopropane-1-carboxylate synthase isolated from tomato fruits

1-Aminocyclopropane-1-carboxylate (ACC) synthase, which catalyzes the conversion of S-adenosyl-L-methionine (AdoMet) to ACC, is irreversibly inactivated by its substrate AdoMet. AdoMet has two diastereomers with respect to its sulfonium center, (-)-AdoMet and (+)-AdoMet. We prepared (+)- and (-)-AdoMet from a commercial source, and compared their activities as a substrate and as an inactivator of ACC synthase isolated from tomato (Lycopersicon esculentum Mill). fruits. Only (-)-AdoMet produced ACC, whereas both (-)- and (+)-AdoMet inactivated ACC synthase; (+)-AdoMet inactivated the enzyme three times faster than (-)-AdoMet. We have previously shown that ACC synthase was specifically radiolabeled when the enzyme was incubated with S-adenosyl-L-[3,4-14C]methionine. The present results further indicate that S-adenosyl-L-[carboxyl-14C]methionine, but not S-adenosyl-L-[methyl-14C]methionine, radiolabeled the enzyme. These data suggest that the 2-aminobutyric acid portion of AdoMet is linked to ACC synthase during the autoinactivation process. A possible mechanism for ACC synthase inactivation by AdoMet is discussed.

Cysteine conjugate beta-lyase of rat kidney cytosol: characterization, immunocytochemical localization, and correlation with hexachlorobutadiene nephrotoxicity

Cysteine conjugate beta-lyase (beta-lyase) was purified to electrophoretic homogeneity from the kidney cytosol of male Wistar rats. The highly purified enzyme exhibited a monomeric molecular weight of 50,000 Da and was active in the alpha-beta elimination of cysteine conjugates including S-(1,2-dichlorovinyl)-L-cysteine (DCVC), S-(1,1,2,2-tetrafluoroethyl)-L-cysteine (TFEC), and S-(2-benzothiazolyl)-L-cysteine, particularly toward DCVC and TFEC. The purified enzyme also exhibited glutamine transaminase K activity with phenylalanine and alpha-keto-gamma-methiolbutyrate as substrates. An antibody was raised to the purified rat protein in sheep and the crude immune serum affinity purified, yielding a specific antibody that recognized only the beta-lyase protein in whole kidney homogenates. Immunocytochemical studies on rat kidney sections stained with the purified antibody revealed that the cytosolic beta-lyase enzyme was mainly localized in the pars recta of the proximal tubule in untreated rats. This localization is coincident with the site-specific kidney necrosis produced by hexachloro-1,3-butadiene (HCBD). These results indicate that the tissue localization of beta-lyase in the proximal tubule plays an important role in determining the specific nephrotoxicity produced by halogenated alkenes such as HCBD.

Cystathionase: high-performance liquid chromatography. Molecular cloning in lambda gt11. Nonradioactive immunodetection of fusion protein

A method of purification of rat liver cystathionase by high-performance liquid chromatography (HPLC) utilizing non-ideal gel filtration method is proposed. Resolution factors-flow rate, pH values, ionic strength of the mobile phase-were optimized. Antibodies to the enzyme were purified using an immunosorbent synthesized on the basis of epoxylated Toyopearl-65. Radioimmunoassay and immunoblotting demonstrated antibody monospecificity towards cystathionase. These monospecific antibodies were utilized for detecting enzyme amounts (up to 30 pg) using the avidin-biotin system. Rat cDNA expression library in phage lambda gt11 was screened. The cystathionase cDNA clone was isolated, and the structure of the insert was determined.