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PubMed1975

[A change in the activity of the beta-phenylpropionic acid conversion enzyme in Escherichia coli under the influence of transmissive plasmids of Salmonella heidelberg].

The activity of the enzyme of the conversion of beta-phenylpropionic acid was studied in the strains of Escherichia coli serotypes 055:K59:H2 and O111:K58:H2 used as recipients via transmission of R- and Col-plasmids by conjugation in vitro. The activity of this enzyme was determined by modified method of Ben Hamida [3]. The wild type strain of Salmonella heidelberg carrying ColIb plasmid and preliminary obtained R1-19 plasmid from E. coli J 5-3 was used as a donor. The activity of the enzyme of conversion of beta-phenylpropionic acid in recombinants carrying R1-19ColIb plasmids was 3-5 times lower as compared with the original recipient. The colour reaction drived under the growth of original bacterial strains in the nutrient broth agar contained beta-phenylpropionic acid at the final concentration of 20 mg% was completely inhibited with that recombinants. The activity of this enzyme in recombinants carrying only R1-19 or ColIb plasmid remains unchanged.

Conjugation, Genetic↗
PubMed1976

Acyl carrier protein metabolism and regulation of fatty acid biosynthesis by Lactobacillus plantarum.

Endogenous fatty acid biosynthesis in the bacterium Lactobacillus plantarum is greatly decreased upon addition of exogenous fatty acids (Henderson, T.A., and McNeil, J.J. (1966) Biochem. Biophys. Res. Commun. 25, 662-669). We have demonstrated the presence of five pantothenate-containing compounds in L. plantarum which have been identified by co-chromatography with authentic samples: pantothenate, 4'-phosphopantetheine, 3'-dephosphocoenzyme A, coenzyme A, and acyl carrier protein (ACP). The concentrations of the above pantothenate-containing compounds were found to be: 0.009, 0.13, 0.067, 0.69, and 0.22 nmol/mg of protein, respectively. L. plantarum ACP was shown to have a molecular weight near that of Escherichia coli ACP but to have a lower isoelectric point (pI = 3.75). Oleate in the presence of Triton X-100 was found to reduce the concentration of ACP by 80% with little effect on the concentrations of the other pantothenate-containing compounds. The synthesis of ACP apparently ceased soon after the addition of oleate and the rate of decrease in concentration of ACP was quanitatively consistent with the previously observed rate of decrease in the initial rate of fatty acid biosynthesis in this organism (Weeks, G., and Wakil, S.J. (1970) J. Biol. Chem. 245, 1913-1921). Thus, the change in rate of fatty acid biosynthesis in L. plantarum upon addition of oleate to the medium can be quantitatively related to the concentration of ACP (and probably to the concentration of co-repressible enzymes of fatty acid biosynthesis).

Biological Transport, Active↗
PubMed1972

Mutants with altered glucose repression of amidase enzymes in Aspergillus nidulans.

Aspergillus nidulans produces acetamidase and formamidase enzymes. The acetamidase is produced in reduced amounts during growth on glucose, whereas the formamidase is not greatly affected. Mutations in a gene, amdT, which affect glucose repression of amidases are described. One of these, amdT102, causes the acetamidase to be no longer subject to glucose repression and also affects ability to synthesize formamidase. The other, amdT19, results in both the formamidase and the acetamidase being subject to abnormally strong glucose repression, and also in increased maximal acetamidase activities. The dominance relationships at the amdT locus have been investigated. It is suggested that the amdT gene may play a positive role in controlling amidase synthesis.

Acetamides↗
PubMed1968

Common element in the repression control of enzymes of histidine and aromatic amino acid biosynthesis in Bacillus subtilus.

Single-step mutants of Bacillus subtilis derepressed for enzymes of both aromatic amino acid and histidine biosynthesis were isolated. These mutants occur at a frequency of 10(-6) per cell per generation. All histidine enzymes as well as all enzymes of aromatic acid synthesis which were examined are maximally derepressed. This level cannot be repressed by growth on either histidine or tyrosine. Some of the structural genes which specify the derepressed enzymes are linked to the aromatic cluster; others are unlinked. The significance of these nonrepressible strains is discussed in terms of the mechanism of repression.

Adenosine Triphosphate↗
PubMed1968

Reversible repression of early enzyme synthesis in bacteriophage T4-infected Escherichia coli.

A mutant of Escherichia coli B, defective in its accumulation of K(+), was found to synthesize protein at a rate proportional to the level of this cation in the growth medium. When bacteriophage T4-infected cells were incubated in growth medium containing 1 mm K(+), phage deoxyribonucleic acid (DNA) was synthesized at a rate 25% that of normal, and phage protein was synthesized at a rate of 50% of normal. Deoxycytidine pyrophosphatase, a phage-directed early enzyme, shut off at a level of 55% that of normal when infected cells were incubated in medium containing 1 mm K(+). However, deoxycytidine pyrophosphatase synthesis resumed in these cells when they were shifted to medium containing the normal K(+) concentration (33 mm). DNA synthesis also attained the rate characteristic of this K(+) concentration. These results suggest that phage DNA synthesis is not sufficient to repress early protein formation and also indicate that the inhibitor of early protein formation is an early function whose synthesis is sensitive to the same repression as that of the early proteins.

Chloramphenicol↗
PubMed1978

[Effect of platinum derivatives on the inducible and repressible liver microsomal enzyme systems in the rat: inhibition of zoxazolamine-hydroxylase and induction of dimethyl-nitrosamine demethylase isoenzymes by cis-dichlorodiamine platinum (cis-PtCl2(NH3)2) and ammonium hexachloroplatinum (PtC16(NH4)2)].

Two platinum derivatives, cis-PtCl2(NH3)2 and PtCl6(NH4)2 have been studied for their effects on the Rat on cytochrome P450 in hepatic parenchyma on zoxazolamine-hydroxylase, a typical inducible system and on the two isoenzymes of dimethyl-nitrosamine demethylase, typical repressible systems. The inhibitory effect of PtCl6(NH4)2 on zoxazolamine-hydroxylase activity, previously shown by the authors, has been confirmed. The cis-PtCl2(NH3)2 also significantly inhibits zoxazolamine-hydroxylase activity. On the other hand, both of the platinum derivatives decrease cytochrome P450 level and enhance the dimethyl-nitrosamine metabolism. These various effects and their relationship are discussed.

Animals↗
PubMed1969

Catabolite repression of the lac operon. Separt epressionof two enzymes.

1. Catabolite repression of beta-galactosidase and of thiogalactoside transacetylase was studied in several strains of Escherichia coli K 12, in an attempt to show whether a single site within the structural genes of the lac operon co-ordinately controls translational repression for the two enzymes. In all experiments the rate of synthesis of the enzymes was compared in glycerol-minimal medium and in glucose-minimal medium. 2. In a wild-type strain, glucose repressed the synthesis of the two enzymes equally. 3. The possibility that repression was co-ordinate was investigated by studies of mutant strains that carry deletions in the genes for beta-galactosidase or galactoside permease or both. In all of the strains with deletions, the repression of thiogalactoside transacetylase persisted, and it is concluded that there is no part of the structural gene for beta-galactosidase that is essential for catabolite repression of thiogalactoside transacetylase. 4. Subculture of one strain through several transfers in rich medium greatly increased its susceptibility to catabolite repression by glucose. It is concluded that unknown features of the genotype can markedly affect sensitivity to catabolite repression. 5. These results make it clear that one cannot draw valid conclusions about the effect of known genotypic differences on catabolite repression from a comparison of two separate strains; to study the effect of a particular genetic change in a lac operon it is necessary to construct a partially diploid strain so that catabolite repression suffered by one lac operon can be compared with that suffered by another. 6. Four such partial diploids were constructed. In all of them catabolite repression of beta-galactosidase synthesized by one operon was equal in extent to catabolite repression of thiogalactoside transacetylase synthesized by the other. 7. Taken together, these results suggest that catabolite repression of beta-galactosidase and thiogalactoside transacetylase is separate but equal.

Acyltransferases↗
PubMed2004

HPr kinase/phosphorylase, a Walker motif A-containing bifunctional sensor enzyme controlling catabolite repression in Gram-positive bacteria.

Carbon catabolite repression (CCR) in Gram-positive bacteria is regulated by the bifunctional enzyme HPr kinase/phosphorylase (HprK/P). This enzyme catalyses the ATP- as well as the pyrophosphate-dependent phosphorylation of Ser-46 in HPr, a phosphocarrier protein of a sugar transport and phosphorylation system. HprK/P also catalyses the pyrophosphate-producing, inorganic phosphate-dependent dephosphorylation (phosphorolysis) of seryl-phosphorylated HPr (P-Ser-HPr). P-Ser-HPr functions as catabolite co-repressor by interacting with the LacI/GalR-type repressor, catabolite control protein A (CcpA), and allowing it to bind to operator sites preceding catabolite-regulated transcription units. HprK/P thus indirectly controls the expression of about 10% of the genes of Gram-positive bacteria. The two antagonistic activities of HprK/P are regulated by intracellular metabolites, which change their concentration in response to the absence or presence of rapidly metabolisable carbon sources (glucose, fructose, etc.) in the growth medium. Biochemical and structural studies revealed that HprK/P exhibits no similarity to eukaryotic protein kinases and that it contains a Walker motif A (or P-loop) as nucleotide binding site. Interestingly, HprK/P has a structural fold resembling that in kinases phosphorylating certain low molecular weight substrates such as nucleosides, nucleotides or oxaloacetate. The structures of the complexes of HprK/P with HPr and P-Ser-HPr have also been determined, which allowed proposing a detailed mechanism for the kinase and phosphorylase functions of HprK/P.

Amino Acid Motifs↗
PubMed1967

Intracellular concentration of cysteine in Escherichia coli and its relation to repression of the sulphate-activating enzymes.

1. The intracellular cysteine and glutathione concentrations were measured in Escherichia coli under a variety of growth conditions. 2. An inverse relation between intracellular cysteine concentration and the specific activity of the sulphate-activating enzymes was found. 3. This is compatible with the view that the intracellular cysteine concentration controls the rate of synthesis of these enzymes.

Adenine Nucleotides↗
PubMed1986

Coordinate repression of arginine aminopeptidase and three enzymes of the arginine deiminase pathway in Streptococcus mitis.

Streptococcus mitis contains two arginine aminopeptidases (I and II) as an arginine-supplying system and the arginine deiminase pathway as an arginine-utilizing system. The levels of arginine aminopeptidase I and three enzymes of the arginine deiminase pathway were suppressed by glucose in an apparently coordinate manner. Enzyme II appeared to be constitutive.

Aminopeptidases↗