Regulation of tyramine oxidase synthesis in Klebsiella aerogenes

The Norepinephrine Metabolite 3,4-Dihydroxymandelic Acid Is Produced by the Commensal Microbiota and Promotes Chemotaxis and Virulence Gene Expression in Enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) is a commonly occurring foodborne pathogen responsible for numerous multistate outbreaks in the United States. It is known to infect the host gastrointestinal tract, specifically, in locations associated with lymphoid tissue. These niches serve as sources of enteric neurotransmitters, such as epinephrine and norepinephrine, that are known to increase virulence in several pathogens, including enterohemorrhagic E. coli The mechanisms that allow pathogens to target these niches are poorly understood. We previously reported that 3,4-dihydroxymandelic acid (DHMA), a metabolite of norepinephrine produced by E. coli, is a chemoattractant for the nonpathogenic E. coli RP437 strain. Here we report that DHMA is also a chemoattractant for EHEC. In addition, DHMA induces the expression of EHEC virulence genes and increases attachment to intestinal epithelial cells in vitro in a QseC-dependent manner. We also show that DHMA is present in murine gut fecal contents and that its production requires the presence of the commensal microbiota. On the basis of its ability to both attract and induce virulence gene expression in EHEC, we propose that DHMA acts as a molecular beacon to target pathogens to their preferred sites of infection in vivo.

Microbial Endocrinology in the Pathogenesis of Infectious Disease

Microbial endocrinology represents the intersection of two seemingly disparate fields, microbiology and neurobiology, and is based on the shared presence of neurochemicals that are exactly the same in host as well as in the microorganism. The ability of microorganisms to not only respond to, but also produce, many of the same neurochemicals that are produced by the host, such as during periods of stress, has led to the introduction of this evolutionary-based mechanism which has a role in the pathogenesis of infectious disease. The consideration of microbial endocrinology-based mechanisms has demonstrated, for example, that the prevalent use of catecholamine-based synthetic drugs in the clinical setting contributes to the formation of biofilms in indwelling medical devices. Production of neurochemicals by microorganisms most often employs the same biosynthetic pathways as those utilized by the host, indicating that acquisition of host neurochemical-based signaling system in the host may have been acquired due to lateral gene transfer from microorganisms. That both host and microorganism produce and respond to the very same neurochemicals means that there is bidirectionality contained with the theoretical underpinnings of microbial endocrinology. This can be seen in the role of microbial endocrinology in the microbiota-gut-brain axis and its relevance to infectious disease. Such shared pathways argue for a role of microorganism-neurochemical interactions in infectious disease.

Syncephalastrum racemosum amine oxidase with high catalytic efficiency toward ethanolamine and its application in ethanolamine determination

Our screening study yielded a copper amine oxidase (SrAOX) from Syncephalastrum racemosum, which showed much higher affinity and catalytic efficiency toward ethanolamine (EA) than any other amine oxidase (AOX). Following purification of the enzyme to electrophoretic homogeneity from a cell-free extract, the maximum activity toward EA was detected at pH 7.2-7.5 and 45 °C. The SrAOX complementary DNA (cDNA) was composed of a 2052-bp open reading frame encoding a 683-amino acid protein with a molecular mass of 77,162 Da. The enzyme functions as a homodimer. The deduced amino acid sequence of SrAOX showed 55.3 % identity to Rhizopus delemar AOX and contains two consensus sequences of Cu-AOX, NYDY, and HHQH, suggesting SrAOX is a type 1 Cu-AOX (i.e., a topaquinone enzyme). Structural homology modeling showed that residues (112)ML(113), (141)FADTWG(146) M158, and N318 are unique, and T144 possibly characterizes the substrate specificity of SrAOX. The recombinant enzyme (rSrAOX) was produced using Escherichia coli. Steady-state kinetic analysis of rSrAOX activity toward EA (pH 7.5 and 45 °C) gave K m and k cat values of 0.848 ± 0.009 mM and 9.11 ± 0.13 s(-1), respectively. The standard curves were linear between 0.1 and 2 mM EA, and 10 μg mL(-1)-2.5 mg mL(-1) (15 μM-3.6 mM) phosphatidylethanolamine using Streptomyces chromofuscus phospholipase D, respectively, was sufficiently sensitive for clinical use.

Live attenuated S. Typhimurium vaccine with improved safety in immuno-compromised mice

Live attenuated vaccines are of great value for preventing infectious diseases. They represent a delicate compromise between sufficient colonization-mediated adaptive immunity and minimizing the risk for infection by the vaccine strain itself. Immune defects can predispose to vaccine strain infections. It has remained unclear whether vaccine safety could be improved via mutations attenuating a vaccine in immune-deficient individuals without compromising the vaccine's performance in the normal host. We have addressed this hypothesis using a mouse model for Salmonella diarrhea and a live attenuated Salmonella Typhimurium strain (ssaV). Vaccination with this strain elicited protective immunity in wild type mice, but a fatal systemic infection in immune-deficient cybb^−/−nos2^−/− animals lacking NADPH oxidase and inducible NO synthase. In cybb^−/−nos2^−/− mice, we analyzed the attenuation of 35 ssaV strains carrying one additional mutation each. One strain, Z234 (ssaV SL1344_3093), was >1000-fold attenuated in cybb^−/−nos2^−/− mice and ≈100 fold attenuated in tnfr1^−/− animals. However, in wt mice, Z234 was as efficient as ssaV with respect to host colonization and the elicitation of a protective, O-antigen specific mucosal secretory IgA (sIgA) response. These data suggest that it is possible to engineer live attenuated vaccines which are specifically attenuated in immuno-compromised hosts. This might help to improve vaccine safety.

The 3,4-dihydroxyphenylacetic acid catabolon, a catabolic unit for degradation of biogenic amines tyramine and dopamine in Pseudomonas putida U

Degradation of tyramine and dopamine by Pseudomonas putida U involves the participation of twenty one proteins organized in two coupled catabolic pathways, Tyn (tynABFEC tynG tynR tynD, 12 338 bp) and Hpa (hpaR hpaBC hpaHI hpaX hpaG1G2EDF hpaA hpaY, 12 722 bp). The Tyn pathway catalyses the conversion of tyramine and dopamine into 4-hydroxyphenylacetic acid (4HPA) and 3,4-dihydroxyphenylacetic acid (3,4HPA) respectively. Together, the Tyn and Hpa pathways constitute a complex catabolic unit (the 3,4HPA catabolon) in which 3,4HPA is the central intermediate. The genes encoding Tyn proteins are organized in four consecutive transcriptional units (tynABFEC, tynG, tynR and tynD), whereas those encoding Hpa proteins constitute consecutive operons (hpaBC, hpaG1G2EDF, hpaX, hpaHI) and three independent units (hpaA, hpaR and hpaY). Genetic engineering approaches were used to clone tyn and hpa genes and then express them, either individually or in tandem, in plasmids and/or bacterial chromosomes, resulting in recombinant bacterial strains able to eliminate tyramine and dopamine from different media. These results enlarge our biochemical and genetic knowledge of the microbial catabolic routes involved in the degradation of aromatic bioamines. Furthermore, they provide potent biotechnological tools to be used in food processing and fermentation as well as new strategies that could be used for pharmacological and gene therapeutic applications in the near future.

Histamine and tyramine degradation by food fermenting microorganisms

Microorganisms suitable for food fermentation were examined with regard to their potential to degrade histamine and tyramine. Out of 64 lactic acid bacteria evaluated in this study, 27 degraded histamine and one tyramine, respectively, with low activity. Among 32 strains of Brevibacterium linens and coryneform bacteria, 21 exhibited histamine and tyramine oxidase activity. None of 20 strains of Staphylococcus carnosus tested degraded histamine or tyramine. One strain out of nine strains of Geotrichum candidum degraded tyramine slightly. Among 44 strains of Micrococcus sp. examined, 17 degraded either one or two biogenic amines. In this study Micrococcus varians (M. varians) LTH 1540 exhibited the highest tyramine oxidase activity of all strains tested and was therefore investigated in detail. The enzyme was found to be located in the cytoplasm and was not membrane bound. The reaction end product p-hydroxyphenyl acetic acid was detected by HPLC analysis. An activity staining for the amine oxidase in a native polyacrylamide gel based on the formation of H2O2 during amine oxidation was developed. Resting cells of the strain exhibited optimal tyramine oxidase activity at a pH of 7 at 37-40 degrees C. The enzyme in the cell free extract had a pH optimum between 7-8. The enzyme activity was decreased by NaCl, glucose and hydralazine. Phenylethylamine and tryptamine were oxidized at lower concentrations than tyramine. The potential for amine degradation was not found to be associated with that of formation of biogenic amines, as 23 microorganisms with the ability to metabolise biogenic amines exhibited no decarboxylase activity toward histidine, tyrosine, phenylalanine, lysine or ornithine.

Distribution of amine oxidases and amine dehydrogenases in bacteria grown on primary amines and characterization of the amine oxidase from Klebsiella oxytoca

The bacteria Klebsiella oxytoca LMD 72.65 (ATCC 8724), Arthrobacter P1 LMD 81.60 (NCIB 11625), Paracoccus versutus LMD 80.62 (ATCC 25364), Escherichia coli W LMD 50.28 (ATCC 9637), E. coli K12 LMD 93.68, Pseudomonas aeruginosa PAO1 LMD 89.1 (ATCC 17933) and Pseudomonas putida LMD 68.20 (ATCC 12633) utilized primary amines as a carbon and energy source, although the range of amines accepted varied from organism to organism. The Gram-negative bacteria K. oxytoca and E. coli as well as the Gram-positive methylotroph Arthrobacter P1 used an oxidase whereas the pseudomonads and the Gram-negative methylotroph Paracoccus versutus used a dehydrogenase for amine oxidation. K. oxytoca utilized several primary amines but showed a preference for those containing a phenyl group moiety. Only a single oxidase was used for oxidation of the amines. After purification, the following characteristics of the enzyme indicated that it belonged to the group of copper-quinoprotein amine oxidase (EC 1.4.3.6): the molecular mass (172,000 Da) of the homodimeric protein; the UV/visible and EPR spectra of isolated and p-nitrophenylhydrazine-inhibited enzyme; the presence and the content of copper and topaquinone (TPQ). The amine oxidase appeared to be soluble and localized in the periplasm, but catalase and NAD-dependent aromatic aldehyde dehydrogenase, enzymes catalysing the conversion of its reaction products, were found in the cytoplasm. From the amino acid sequence of the N-terminal part as well as that of a purified peptide, it appears that K. oxytoca produces a copper-quinoprotein oxidase which is very similar to that found in other Enterobacteriaceae.

On the amine oxidases of Klebsiella aerogenes strain W70

Klebsiella aerogenes W70 was reported previously to produce a membrane-associated tyramine oxidase (TynA) that did not act on 2-phenylethylamine. Subsequently, a gene cloned from K. aerogenes W70 produced a soluble amine oxidase (MaoA) that acted readily on 2-phenylethylamine and tyramine. This enzyme appeared to be equivalent to a 2-phenylethylamine oxidase of Escherichia coli K-12 (MaoA) but was assumed to be the originally described K. aerogenes W70 tyramine oxidase (TynA). However, as described here, whole cells and cell-free extracts of K. aerogenes W70 showed only the tyramine oxidase (TynA) that is inactive against 2-phenylethylamine and not the maoA gene product. It seems that the organism has two amine oxidase genes, tynA and maoA, but only tynA is expressed. Hence, data relating to the expression of the K. aerogenes W70 tynA gene cannot be assumed to apply to the maoA gene of E. coli K-12 because they encode different enzymes.

maoB, a gene that encodes a positive regulator of the monoamine oxidase gene (maoA) in Escherichia coli

The structural gene for copper- and topa quinone-containing monoamine oxidase (maoA) and an unknown amine oxidase gene have been located at 30.9 min on the Escherichia coli chromosome. Deletion analysis showed that the unknown gene was located within a 1.1-kb cloned fragment adjacent to the maoA gene. The nucleotide sequence of this fragment was determined, and a single open reading frame (maoB) consisting of 903 bp was found. The gene encoded a polypeptide with a predicted molecular mass of 34,619 Da which was correlated with the migration on a sodium dodecyl sulfate-polyacrylamide gel. The predicted amino acid sequence of the MaoB protein was identical to the NH2-terminal amino acid sequence derived by Edman degradation of the protein synthesized under the self-promoter. No homology of the nucleotide sequence of maoB to the sequences of any reported genes was found. However, the amino acid sequence of MaoB showed a high level of homology with respect to the helix-turn-helix motif of the AraC family in its C terminus. The homology search and disruption of maoA on the chromosome led to the conclusion that MaoB is a transcriptional activator of maoA but not an amine oxidase. The consensus sequence of the cyclic AMP-cyclic AMP receptor protein complex binding domain was adjacent to the putative promoter for the maoB gene. By use of lac gene fusions with the maoA and maoB genes, we showed that the maoA gene is regulated by tyramine and MaoB and that the expression of the maoB gene is subject to catabolite repression. Thus, it seems likely that tyramine and the MaoB protein activate the transcription of maoA by binding to the regulatory region of the maoA gene.

Microbial metabolism of sulfur- and phosphorus-containing xenobiotics

The enzymes involved in the microbial metabolism of many important phosphorus- or sulfur-containing xenobiotics, including organophosphate insecticides and precursors to organosulfate and organosulfonate detergents and dyestuffs have been characterized. In several instances their genes have been cloned and analysed. For phosphonate xenobiotics, the enzyme system responsible for the cleavage of the carbon-phosphorus bond has not yet been observed in vitro, though much is understood on a genetic level about phosphonate degradation. Phosphonate metabolism is regulated as part of the Pho regulon, under phosphate starvation control. For organophosphorothionate pesticides the situation is not so clear, and the mode of regulation appears to depend on whether the compounds are utilized to provide phosphorus, carbon or sulfur for cell growth. The same is true for organosulfonate metabolism, where different (and differently regulated) enzymatic pathways are involved in the utilization of sulfonates as carbon and as sulfur sources, respectively. Observations at the protein level in a number of bacteria suggest that a regulatory system is present which responds to sulfate limitation and controls the synthesis of proteins involved in providing sulfur to the cell and which may reveal analogies between the regulation of phosphorus and sulfur metabolism.

moaR, a gene that encodes a positive regulator of the monoamine regulon in Klebsiella aerogenes

We cloned and sequenced a Klebsiella aerogenes gene (moaR) for activation of arylsulfatase synthesis by tyramine. This gene was cloned by complementation of a K. aerogenes mutant in which tyramine fails to relieve the arylsulfatase repression caused by sulfur compounds. The moaR gene also activated induction of the synthesis of both tyramine oxidase and the 30-kDa protein that is specifically induced by high concentrations of tyramine or catecholamines. The moaR gene on the chromosome of the wild-type strain of K. aerogenes was disrupted by homologous recombination with a plasmid containing the inactivated moaR. The resultant mutant showed the same phenotype as previously isolated atsT mutant strains that are negative for the derepressed synthesis of arylsulfatase. In this mutant strain, tyramine also failed to induce the synthesis of tyramine oxidase or the production of a 30-kDa protein. The moaR gene is capable of encoding a protein of 26,238 Da. The putative MoaR protein has a helix-turn-helix motif in its C terminus. Thus, it seems likely that the MoaR protein regulates the operons by binding to the regulatory region of the monoamine regulon. The MoaR protein is subject to autogenous control, which was shown by use of a moaR'-lacZ transcriptional fusion.

A monoamine-regulated Klebsiella aerogenes operon containing the monoamine oxidase structural gene (maoA) and the maoC gene

The Klebsiella aerogenes gene maoA, which is involved in the synthesis of monoamine oxidase, was induced by tyramine and the related compounds, subjected to catabolite and ammonium ion repression, and cloned. The nucleotide sequence of the region involved in monoamine oxidase synthesis was determined. Two open reading frames, the maoA gene and a hitherto unknown gene (maoC), were found. These are located between a potential promoter sequence and a transcriptional terminator sequence. A region of the Escherichia coli chromosome that was highly homologous to the Klebsiella maoA gene was found. The potential maoA gene is located at 30.9 min on the E. coli chromosome. Analysis of the amino acid sequences of the first 11 amino acids from the N terminus of the purified monoamine oxidase agrees with those deduced from the nucleotide sequence of the maoA gene. The leader peptide extends over 30 amino acids and has the characteristics of a signal sequence. Primer extension and S1 nuclease mapping of transcripts generated in vivo suggests that the tyramine-induced mRNA starts at a site 62 bases upstream from the ATG initiation codon of the maoC gene. In the putative promoter region, a high degree of similarity to the consensus sequence for the binding site of cyclic AMP receptor protein was found. Thus, the mao region is composed of two cistrons, and the mao operon is regulated by monoamine compounds, glucose, and ammonium ions.

Initial catabolism of aromatic biogenic amines by Pseudomonas aeruginosa PAO: pathway description, mapping of mutations, and cloning of essential genes

Pseudomonas aeruginosa PAO1 was able to utilize several aromatic biogenic amines as sole sources of carbon or nitrogen. These included the phenethylamines tyramine and dopamine and the phenethanolamines octopamine, synephrine, and norepinephrine. Initial catabolism of the phenethylamines was mediated by a membrane-bound tyramine dehydrogenase which produced 4-hydroxyphenylacetaldehyde (4HPAL) with tyramine as the substrate. The enzyme was induced by growth with both classes of amines. Initial catabolism of octopamine (except when present as the sole source of carbon and nitrogen) was mediated by a soluble enzyme with activity against the phenethanolamines but not against tyramine or dopamine. The product of the reaction with octopamine as substrate was also 4HPAL. Addition of NAD to reaction mixtures yielded 4-hydroxyphenylacetic acid and NADH. These activities, octopamine hydrolyase and 4-HPAL dehydrogenase (measured as a combined activity, OCAH-4HPALDH), were only induced by growth with phenethanolamines. However, the combined activities were not observed in extracts from cells grown with octopamine as the sole source of carbon and nitrogen, suggesting that an alternate pathway is used under this growth condition. Two independently isolated mutant strains were unable to utilize tyramine as a sole source of carbon or nitrogen. These mutants were also unable to utilize dopamine but grew at wild-type rates on the phenethanolamines. The mutations were mapped at about 70 min on the PAO1 chromosome with the chromosome-mobilizing plasmid R68.45, and both were linked to the catA1, mtu-9002, tyu-9009, and puuE mutations. DNA complementing both of the mutations was cloned on a single BamHI fragment approximately 13.8 kilobase pairs in length. Analysis of a subcloned fragment showed that the two mutations were in different genes.

Regulation of derepressed synthesis of arylsulfatase by tyramine oxidase in Salmonella typhimurium

The participation of tyramine oxidase in the regulation of arylsulfatase synthesis in Salmonella typhimurium was studied. Arylsulfatase synthesis was repressed by inorganic sulfate, cysteine, methionine, or taurine. This repression was relieved by tyramine, octopamine, or dopamine, which induced tyramine oxidase synthesis, although the level of arylsulfatase activity was very low. The induction of tyramine oxidase and derepression of arylsulfatase by tyramine were strongly inhibited by glucose and ammonium chloride, and the repression of both enzymes was relieved by use of xylose as a carbon source after consumption of glucose or by use of tyramine as the sole source of nitrogen, irrespective of the carbon source used. The initial rates of tyramine uptake by cells grown with glucose and xylose were similar. Results with tyramine oxidase-constitutive mutants showed that constitutive expression of the tyramine oxidase gene resulted in derepression of arylsulfatase synthesis in the absence of tyramine. Thus, catabolite and ammonium repressions of arylsulfatase synthesis and the induction of the enzyme by tyramine seem to reflect the levels of tyramine oxidase synthesis. These results in S. typhimurium support our previous finding that the specific regulation system of arylsulfatase synthesis by tyramine oxidase is conserved in enteric bacteria.

Genetic control of tyramine oxidase, which is involved in derepressed synthesis of arylsulfatase in Klebsiella aerogenes

Mutants of Klebsiella aerogenes with three types of mutations affecting regulation of tyramine oxidase were isolated by a simple selection method. In the first type, the mutation (tynP) was closely linked to the structural gene for tyramine oxidase tynA). The order of mutation sites was atsA-tynP-tynA. In the second type, the mutation that relieves catabolite repression of the syntheses of several catabolite repression-sensitive enzymes are not linked to the tyn gene by P1 transduction. These strains contained high levels of cyclic adenosine 5'-monophosphate when grown on glucose. The third type of mutation, in which tyramine oxidase was synthesized constitutively, was shown by genetic analysis to involve mutations of tynP and tynR. The tynR gene was not linked to tynA. Results using the constitutive mutants showed that the constitutive expression of the tynA gene resulted in depression of arylsulfatase synthesis in the absence of tyramine.

Formation and Purification of Serratia marcescens Arylsulfatase

The effects of culture conditions on arylsulfatase production by six strains of the genus Serratia were studied. Synthesis of arylsulfatases in all six strains was repressed in media with inorganic sulfate or methionine as the sole source of sulfur and derepressed by the addition of tyramine. Serratia marcescens IFO 3046 grew most rapidly and produced a high level of arylsulfatase when cultured on mannitol with inorganic sulfate and tyramine. The derepressed synthesis of arylsulfatase in S. marcescens was not subject to strong catabolite repression. The molecular weight of purified arylsulfatase was determined to be between 46,000 and 49,000. Arylsulfatase from S. marcescens differed in K m and V max values, substrate specificities, fluoride inhibition, and electrophoretic mobility from the enzyme from K. aerogenes , but had the same molecular weight as the latter.

Distribution of membrane-bound monoamine oxidase in bacteria

The distribution of membrane-bound monoamine oxidase in 30 strains of various bacteria was studied. Monoamine oxidase was determined by using an ammonia-selective electrode; analyses were sensitive and easy to perform. The enzyme was found in some strains of the family Enterobacteriaceae, such as Klebsiella, Enterobacter, Escherichia, Salmonella, Serratia, and Proteus. Among strains of other families of bacteria tested, only Pseudomonas aeruginosa IFO 3901, Micrococcus luteus IFO 12708, and Brevibacterium ammoniagenes IAM 1641 had monoamine oxidase activity. In all of these bacteria except B. ammoniagenes, monoamine oxidase was induced by tyramine and was highly specific for tyramine, octopamine, dopamine, and norepinephrine. The enzyme in two strains oxidized histamine or benzylamine. Correlations between the distributions of membrane-bound monoamine oxidase and arylsulfatase synthesized in the presence of tyramine were discussed.

Arylsulfatase in Salmonella typhimurium: detection and influence of carbon source and tyramine on its synthesis

Arylsulfatase synthesis was shown to occur in Salmonella typhimurium LT2. The enzyme had a molecular weight of approximately 50,000 and was separated into five forms by isoelectrofocusing. The optimal pH for substrate hydrolysis was pH 6.7, with Michaelis constants for nitrocatechol sulfate and nitrophenyl sulfate being 4.1 and 7.9 mM, respectively. Enzyme synthesis was strongly influenced by the presence of tyramine in the growth medium. The uptake of [14C]tyramine and arylsulfatase synthesis were initiated during the second phase of a diauxie growth response, when the organism was cultured with different carbon sources. Adenosine 3',5'-cyclic monophosphoric acid enhanced the uptake of tyramine and the levels of arylsulfatase synthesized. However, the addition of glucose and glycerol to organisms actively transporting tyramine and synthesizing enzyme caused a rapid inhibition of both of these processes. This inhibition was not reversed by adding adenosine 3',5'-cyclic monophosphoric acid. The results suggest that the effect of the carbon source on tyramine transport and arylsulfatase synthesis may be explained in terms of inducer exclusion.

Genetic mapping of tyramine oxidase and arylsulfatase genes and their regulation in intergeneric hybrids of enteric bacteria

The genes for arylsulfatase (atsA) and tyramine oxidase (tynA) have been mapped in Klebsiella aerogenes by P1 transduction. They are linked to gdhD and trp in the order atsA-tynA-gdhD-trp-pyrF. Complementation analysis using F' episomes from Escherichia coli suggested an analogous location of these genes in E. coli, although arylsulfatase activity was not detected in E. coli. P1 phage and F' episomes were used to create intergeneric hybrid strains of enteric bacteria by transfer of the ats and tyn genes between K. aerogenes, E. coli, and Salmonella typhimurium. Intergeneric transduction of the tynK gene from K. aerogenes to an E. coli restrictionless strain was one to two orders less frequent than that of the leuK gene. The tyramine oxidase of E. coli and S. typhimurium in regulatory activity resemble very closely the enzyme of K. aerogenes. The atsE gene from E. coli was expressed, and latent arylsulfatase protein was formed in K. aerogenes and S typhimurium. The results of tyramine oxidase and arylsulfatase synthesis in intergeneric hybrids of enteric bacteria suggest that the system for regulation of enzyme synthesis is conserved more than the structure or function of enzyme protein during evolution.

Immunological study of the regulation of cellular arylsulfatase synthesis in Klebsiella aerogenes

Regulation of cellular arylsulfatase synthesis in Klebsiella aerogenes was analyzed by immunological techniques. Antibody directed against the purified arylsulfatase from K. aerogenes W70 was obtained from rabbits and characterized by immunoelectrophoresis, double-diffusion, quantitative precipitation, and enzyme neutralization tests. Arylsulfatase was located in the periplasmic space when the wild-type strain was cultured with methionine or with inorganic sulfate plus tyramine, but not with inorganic sulfate without tyramine, as the sole sulfur source. Tyramine oxidase was retained in the membrane fraction prepared from cells grown in the presence of tyramine. Arylsulfatase protein was not synthesized in the presence of tyramine and inorganic sulfate by mutant K611, which is deficient in tyramine oxidase (tynA). We conclude that the expression of the arylsulfatase gene (atsA) is regulated by the expression of tynA and that inorganic sulfate serves as a corepressor. In addition, strains mutated in the atsA gene were analyzed by using antibody.

Genetic control of arylsulfatase synthesis in Klebsiella aerogenes

It was shown that at least four genes are specifically responsible for arylsulfatase synthesis in Klebsiella aerogenes. Mutations at chromosome site atsA result in enzymatically inactive arylsulfatase. Mutants showing constitutive synthesis of arylsulfatase (atsR) were isolated by using inorganic sulfate or cysteine as the sulfur source. Another mutation in which repression of arylsulfatase by inorganic sulfate or cysteine could not be relieved by tyramine was determined by genetic analysis to be on the tyramine oxidase gene (tyn). This site was distinguished from the atsC mutation site, which is probably concerned with the action or synthesis of corepressors of arylsulfatase synthesis. Genetic analysis with transducing phage PW52 showed that the order of mutation sites was atsC-atsR-atsA-tynA-tynB. On the basis of these results and previous physiological findings, we propose a new model for regulation of arylsulfatase synthesis.

Tyramine oxidase and regulation of arylsulfatase synthesis in Klebsiella aerogenes

The participation of tyramine oxidase in the regulation of arylsulfatase synthesis in Klebsiella aerogenes was studied. Arylsulfatase was synthesized when this organism was grown with methionine or taurine as the sulfur source (nonrepressing conditions) and was repressed by inorganic sulfate or cysteine; this repression was relieved by tyramine and related compounds (derepressing conditions). Under nonrepressing conditions, arylsulfatase synthesis was not regulated by tyramine oxidase synthesis. However, derepression of arylsulfatase and induction of tyramine oxidase synthesis by tyramine were both antagonized by glucose and other carbohydrate compounds. The derepressed synthesis of arylsulfatase, like that of tyramine oxidase, was released from catabolite repression by use of tyramine as the sole source of nitrogen. A mutant strain that exhibits constitutive synthesis of glutamine synthetase and high levels of histidase when grown in glucose-ammonium medium was subject to the catabolite repression of both tyramine oxidase and arylsulfatase syntheses. Mutants in which repression of arylsulfatase could not be relieved by tyramine could not utilize tyramine as the sole source of nitrogen and were defective in the gene for tyramine oxidase.