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PubMed1975

Assay, characterization, and localization of an enterotoxin produced by Salmonella.

An enterotoxic factor isolated from cultures of Salmonella yielded reproducible results in the suckling mouse model in contrast to other animal models. The enterotoxin appears to possess properties similar to both the heat-stable and heat-labile enterotoxins of Escherichia coli. Preliminary results indicate that the toxin is a protein, is located in the cell wall or outer-membrane fraction, and is difficult to separate from other cell wall constituents.

Amylases↗
PubMed1975

Phage conversion of Shigella flexneri group antigens.

A temperate phage, designated Sf6, has been isolated from Shigella flexneri 3a. Characterization of Sf6 revealed that it possesses the capacity for converting the S. flexneri 3,4 group antigen complex to group factor 6. Serological studies and chemical analysis of lipopolysaccharide from converted strains suggest that group factor 6 is a reflection of an acetylation of the preexisting 3,4 antigen complex. Evidence is provided that the 3,4 group antigen complex functions, at least in part, as a cell surface receptor site for Sf6 adsorption.

Absorption↗
PubMed1972

Isolation and characterization of a native cell wall complex from Neisseria meningitidis.

A cell wall complex has been isolated by gentle methods from both the medium supernatant fluid and whole organisms of Neissieria meningitidis cultures. The two types of preparations have been shown to be essentially identical on the basis of chemical composition, electron microscopy, and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE). Four major components were identified in the complex: group-specific polysaccharide (4 to 10%), protein (45 to 65%), lipopolysaccharide (10 to 25%), and lipid (15 to 30%). The whole complex was found to be immunogenic in rabbits and to elicit production of antibody directed against the protein, the group-specific polysaccharide, and the lipopolysaccharide components. The isolated protein component was also found to be immunogenic in rabbits and to elicit production of serotype-specific antibody. The protein component was found to produce a band pattern in SDS-PAGE that is simple, reproducible, and strain dependent. The lipopolysaccharide component was found to have chemical and biological properties characteristic of bacterial endotoxin. We propose that this complex is representative of the outer trilaminar membrane of the meningococcal cell envelope in its native state.

Animals↗
PubMed2002

Relationship of Yersinia pseudotuberculosis O antigens IA, IIA, and IVB: the IIA gene cluster was derived from that of IVB.

O antigen is part of the lipopolysaccharide present in the outer membrane of gram-negative bacteria and is highly polymorphic. In this study, we obtained sequences of the O-antigen gene clusters for the Yersinia pseudotuberculosis antigens IA, IIA, and IVB. We propose that the IIA gene cluster was derived from the IVB cluster, one of the very few cases in which a parent gene cluster is identified, and that the IA gene cluster could be a hybrid of the IVB and IB gene clusters. All three O antigens contain 6-deoxy-D-mannoheptose, and we identified six genes for the biosynthetic pathway for the precursor of this sugar, GDP-6-deoxy-D-mannoheptose.

Bacterial Proteins↗
PubMed1970

Regulation of the Escherichia coli tryptophan operon by early reactions in the aromatic pathway.

7-Methyltryptophan (7MT) or compounds which can be metabolized to 7MT, 3-methylanthranilic acid (3MA) and 7-methylindole, cause derepression of the trp operon through feedback inhibition of anthranilate synthetase. Tyrosine reverses 3MA or 7-methylindole derepression, apparently by increasing the amount of chorismic acid available to the tryptophan pathway. A mutant isolated on the basis of 3MA resistance (MAR 13) was found to excrete small amounts of chorismic acid and to have a feedback-resistant phenylalanine 3-deoxy-d-arabinoheptulosonic acid-7-phosphate (DAHP) synthetase. Genetic evidence indicates that the mutation conferring 3MA resistance and feedback resistance is very closely linked to aroG, the structural gene for the DAHP synthetase (phe). Since feedback inhibition of anthranilate synthetase by l-tryptophan (or 7MT) is competitive with chorismic acid, alterations in growth conditions (added tyrosine) or in a mutant (MAR 13) which increase the amount of chorismic acid available to the tryptophan pathway result in resistance to 7MT derepression. Owing to this competitive nature of tryptophan feedback inhibition of anthranilate synthetase by chorismic acid, the early pathway apparently serves to exert a regulatory influence on tryptophan biosynthesis.

Aldehyde-Lyases↗
PubMed1971

Purification and properties of 3-deoxy-d-arabinoheptulosonic acid-7-phosphate synthetase (phe) from a lambda aroG+ transductant of Escherichia coli.

By incorporating aroG, the structural gene for 3-deoxy-d-arabinoheptulosonic acid-7-phosphate (DAHP) synthetase (phe), into the genome of a heat-inducible susR60 mutant of phage lambda, it has been possible to increase the intracellular levels of DAHP synthetase (phe) in a lysogenized strain of Escherichia coli some 15-fold over levels found in the wild-type strain. By using this strain, the enzyme has been purified approximately 2,000-fold compared with wild type, and various kinetic parameters of the purified enzyme have been studied. In contrast to previous reports, the inhibition by phenylalanine was found to exhibit sigmoidal kinetics, suggestive of cooperative interactions between phenylalanine binding sites. Stimulation of enzyme activity by Co(2+) was minimal (14%).

Aldehyde-Lyases↗
PubMed1971

Repression of aromatic amino acid biosynthesis in Escherichia coli K-12.

Mutants of Escherichia coli K-12 were isolated in which the synthesis of the following, normally repressible enzymes of aromatic biosynthesis was constitutive: 3-deoxy-d-arabinoheptulosonic acid 7-phosphate (DAHP) synthetases (phe and tyr), chorismate mutase T-prephenate dehydrogenase, and transaminase A. In the wild type, DAHP synthetase (phe) was multivalently repressed by phenylalanine plus tryptophan, whereas DAHP synthetase (tyr), chorismate mutase T-prephenate dehydrogenase, and transaminase A were repressed by tyrosine. DAHP synthetase (tyr) and chorismate mutase T-prephenate dehydrogenase were also repressed by phenylalanine in high concentration (10(-3)m). Besides the constitutive synthesis of DAHP synthetase (phe), the mutants had the same phenotype as strains mutated in the tyrosine regulatory gene tyrR. The mutations causing this phenotype were cotransducible with trpA, trpE, cysB, and pyrF and mapped in the same region as tyrR at approximately 26 min on the chromosome. It is concluded that these mutations may be alleles of the tyrR gene and that synthesis of the enzymes listed above is controlled by this gene. Chorismate mutase P and prephenate dehydratase activities which are carried on a single protein were repressed by phenylalanine alone and were not controlled by tyrR. Formation of this protein is presumed to be controlled by a separate, unknown regulator gene. The heat-stable phenylalanine transaminase and two enzymes of the common aromatic pathway, 5-dehydroquinate synthetase and 5-dehydroquinase, were not repressible under the conditions studied and were not affected by tyrR. DAHP synthetase (trp) and tryptophan synthetase were repressed by tryptophan and have previously been shown to be under the control of the trpR regulatory gene. These enzymes also were unaffected by tyrR.

Aldehyde-Lyases↗
PubMed1971

Phenylalanine and tyrosine biosynthesis in Escherichia coli K-12: mutants derepressed for 3-deoxy-D-arabinoheptulosonic acid 7-phosphate synthetase (phe), 3-deoxy-D-arabinoheptulosonic acid 7-phosphate synthetase (tyr), chorismate mutase T-prephenate dehydrogenase, and transaminase A.

Mutant strains of Escherichia coli have been isolated in which the synthesis of 3-deoxy-d-arabinoheptulosonic acid 7-phosphate (DAHP) synthetase (phe) is derepressed, in addition to those enzymes of tyrosine biosynthesis previously shown to be controlled by the gene tyrR. The major enzyme of the terminal pathway of phenylalanine biosynthesis chorismate mutase-prephenate dehydratase is not derepressed in these strains. Genetic analysis of the mutants shows that the mutation or mutations causing derepression map close to previously reported tyrR mutations. A study of one of the mutations has shown it to be recessive to the wild-type allele in a diploid strain. It is proposed that the tyrR gene product is involved in the regulation of the synthesis of DAHP synthetase (phe) as well as the synthesis of DAHP synthetase (tyr), chorismate mutase-prephenate dehydrogenase, and transaminase A.

Aldehyde-Lyases↗
PubMed1972

Feedback regulation of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthetase from a marine bacterium, Vibrio MB22.

A marine bacterium, Vibrio MB22, has been studied to determine the pattern of feedback regulation of the first enzyme unique to the biosynthesis of the aromatic amino acids, 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthetase. The crude extract was used to study response of the enzyme to various salts as well as possible feedback inhibitors. Ethylenediaminetetraacetic acid was found to be inhibitory to enzyme activity, and only CoCl(2), of the salts tested, allowed full recovery as well as apparent stimulation of the DAHP synthetase activity. The DAHP synthetase activity was inhibited solely by the aromatic amino acids, tyrosine, tryptophan, and phenylalanine, of the possible effectors tested. Further work demonstrated the existence of three isozymes of DAHP synthetase, each primarily inhibited by one of the aromatic amino acids.

Aldehyde-Lyases↗
PubMed1972

Allostery of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthetase in Clostridium: another conserved generic characteristic.

Enzymological studies were done to characterize the allosteric control of 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthetase in three species of Clostridium. Allosteric control was identified as feedback inhibition by phenylalanine and was qualitatively similar for the DAHP synthetases of C. butyricum, C. acetobutylicum, and C. tetanomorphum. Quantitative differences in the enzymology and kinetics of allosteric control distinguished C. tetanomorphum from C. butyricum and C. acetobutylicum. Crude extracts contained apparent proteolytic activity which could be fractionated from DAHP synthetase. The proteolytic activity was more labile than DAHP synthetase in extracts and was progressively inactivated by serial freeze-thaw treatments. Protease activity was at least partially inhibited by phenylmethylsulfonyl-fluoride. The method of comparative allostery of DAHP synthetase distinguishes the genera Bacillus and Clostridium, each having a strongly conserved pattern of regulation for DAHP synthetase. The data reinforce previous conclusions that allosteric control patterns governing the activity of DAHP synthetase are stable, reliable generic characteristics.

Aldehyde-Lyases↗
PubMed1973

Isolation of outer membranes with an ordered array of surface subunits from Acinetobacter.

A method has been developed for the isolation of outer membranes from Acinetobacter sp. strain MJT/F5/199A. Washed cells were broken in a French press and, after deoxyribonuclease and ribonuclease treatment, removal of intact cells, and four washes in 20 mosmol phosphate buffer, pH 7.4, with centrifugation at 25,000 x g for 10 min, preparations of cell wall fragments from which almost all pieces of plasma membrane had been removed resulted. Treatment of the cell walls with lysozyme and further washing, in the presence of 20 mM MgCl(2), yielded preparations of outer membranes. Electron microscopy of freeze-etched preparations shows that a regular pattern of subunits is present on the outer surfaces of intact cells. After negative staining, these subunits are visible on isolated walls and outer membranes; they can be removed by brief treatment with papain. In section, the cell wall structure is that typical of gram-negative bacteria, but the subunits are not detectable on the surface of the outer membrane. The outer membrane retains the appearance of a "unit membrane" in the cell wall, isolated outer membrane, and papain-treated outer membrane fractions. Both cell walls and outer membranes contain a high percentage of protein (76 and 84%, respectively) and not more than 5% carbohydrate, of which glucose and galactose are constitutents. The outer membranes of this Acinetobacter thus differ in structure and composition from those of bacteria in the Enterobacteriaceae.

Alcaligenes↗
PubMed1973

Regulatory gene of phenylalanine biosynthesis (pheR) in Salmonella typhimurium.

4-Fluorophenylalanine-resistant mutants of Salmonella typhimurium were isolated in which synthesis of chorismate mutase P-prephenate dehydratase (specified by pheA) was highly elevated. Transduction analysis showed that the mutation affecting pheA activity was not linked to pheA, and conjugation and merodiploid analysis indicated that it was in the 95- to 100-min region of the Salmonella chromosome. Evidence is presented for the hypothesis that the mutation responsible for constitutivity of chorismate mutase P-prephenate dehydratase occurred in pheR, a gene specifying a cytoplasmic product that affected pheA. pheR mutants were found to carry a second mutation, tyrO. The tyrO mutation acts cis to cause increased levels of the tyrosine biosynthetic enzymes 3-deoxy-d-arabinoheptulosonate 7-phosphate synthetase (tyr) and prephenate dehydrogenase, but it has no effect on regulation of pheA.

Aldehyde-Lyases↗
PubMed1973

Regulation of tyrosine and phenylalanine biosynthesis in Escherichia coli K-12: properties of the tyrR gene product.

A spontaneous amber tyrR mutant has been isolated in which constitutive synthesis of 3-deoxy-d-arabinoheptulosonic acid 7-phosphate (DAHP) synthetase (tyr) and DAHP synthetase (phe) is suppressible by supC(-), supD(-), supF(-) and supU(-). This finding suggests the tyrR gene product is a protein. Derepression of DAHP synthetase (phe) in this and in seven other spontaneous tyrR mutants and in four Mu-1-induced tyrR mutants provides further evidence for the involvement of the tyrR gene product in phenylalanine biosynthesis. Evidence that the tyrR product is a component of repressor, rather than an enzyme involved in its synthesis or modification, comes from a study of a temperature-sensitive tyrR mutant. This mutant is of the thermolabile type, since derepression occurs rapidly and in the presence and absence of growth.

Aldehyde-Lyases↗
PubMed1973

Tyrosine and phenylalanine biosynthesis in Escherichia coli K-12: complementation between different tyrR alleles.

Dominance tests in diploids have confirmed that the product of the tyrR gene is involved in a negative control system affecting the synthesis of both 3-deoxy-d-arabinoheptulosonic acid 7-phosphate (DAHP) synthetase (tyr) and DAHP synthetase (phe). Some tyrR mutants are derepressed for the synthesis of both DAHP synthetase (tyr) and (phe), whereas others are derepressed for the synthesis of DAHP synthetase (tyr) but overrepressed for the synthesis of DAHP synthetase (phe). Complementation tests between these alleles confirm that they are in the same cistron. The allele causing overrepression of enzyme synthesis is dominant over both the wild type and the derepressing allele in diploids.

Aldehyde-Lyases↗