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At least 253 records · Page 14Linked to original sources
PubMed1980

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.

Arylsulfatases↗
PubMed1984

Identification of the purC gene product of Escherichia coli.

The purC region of the Escherichia coli chromosome was isolated from in vivo-derived lambda transducing bacteriophages and cloned in high-copy-number plasmids. The product of the purC gene, phosphoribosylaminoimidazolesuccinocarboxamide synthetase, was identified as a protein with an Mr of ca. 27,000. The level of the protein is increased by more than 60-fold in strains carrying the gene on a high-copy-number plasmid. Purine addition represses the enzyme level in both plasmid- and non-plasmid-containing strains.

Adenine↗
PubMed1986

Cloning and molecular characterization of csm mutations allowing expression of catabolite-repressible operons in the absence of exogenous cyclic AMP.

The cyclic AMP (cAMP) suppressor mutation (csm) of Escherichia coli has been cloned from strain NCR30 in the HindIII-EcoRI site of pBR322. This mutation has been mapped in or near the crp gene. Wild-type crp DNA hybridized to recombinant plasmids pGM5 and pGM25 containing the cloned csm mutation. These recombinant plasmids encoded a protein product of identical molecular weight and charge as that of the wild-type cAMP receptor protein. Transformants of cya crp deletion strains harboring pBM5 or pGM25 exhibited phenotypic characteristics common to strain NCR30. These included the expression of catabolite-repressible enzymes, such as arabinose isomerase, tryptophanase, beta-galactosidase, and threonine deaminase; the expression of chemotactic and motility genes; cAMP sensitivity; and the accumulation of toxic levels of methylglyoxal. DNA sequence analysis indicated that the Csm suppressor phenotype was attributable to the insertion of a guanosine residue 17 base pairs downstream from the termination codon of the crp structural gene. The guanosine insertion is located in the stem region of the presumed transcriptional termination loop. This stem region contained a unique BssHII restriction site which was used to construct an in vitro deletion in the wild-type crp insert in plasmid pHA7. The resulting plasmid, pGM459, renders transformants having a phenotype common to that conferred by the chromosomal or cloned csm mutation. Our results indicate a novel role for the 3' flanking region of the crp structural gene in the expression of the cAMP receptor protein.

Arabinose↗
PubMed2003

FlhD/FlhC is a regulator of anaerobic respiration and the Entner-Doudoroff pathway through induction of the methyl-accepting chemotaxis protein Aer.

The regulation by two transcriptional activators of flagellar expression (FlhD and FlhC) and the chemotaxis methyl-accepting protein Aer was studied with glass slide DNA microarrays. An flhD::Kan insertion and an aer deletion were independently introduced into two Escherichia coli K-12 strains, and the effects upon gene regulation were investigated. Altogether, the flhD::Kan insertion altered the expression of 29 operons of known function. Among them was Aer, which in turn regulated a subset of these operons, namely, the ones involved in anaerobic respiration and the Entner-Doudoroff pathway. In addition, FlhD/FlhC repressed enzymes involved in aerobic respiration and regulated many other metabolic enzymes and transporters in an Aer-independent manner. Expression of 12 genes of uncharacterized function was also affected. FlhD increased gltBD, gcvTHP, and ompT expression. The regulation of half of these genes was subsequently confirmed with reporter gene fusions, enzyme assays, and real-time PCR. Growth phenotypes of flhD and flhC mutants were determined with Phenotype MicroArrays and correlated with gene expression.

Anaerobiosis↗
PubMed1992

Comparison of the E test and microdilution for detection of beta-lactam-resistant mutants that are stably derepressed for type I beta-lactamase.

The activities of cefotaxime, ceftazidime, piperacillin, and aztreonam were compared in the E test and broth microdilution test against 30 gram-negative bacterial mutants derepressed for type I beta-lactamases. The results demonstrated complete agreement between 24-h MICs of 80 to 83% and essential agreement between 24-h MICs of 90 to 97%. When sufficient growth was present for the E test to be read at 6 h, the essential agreement between 6- and 24-h E-test MICs was 100% for ceftazidime, piperacillin, and aztreonam and 85% for cefotaxime.

Anti-Bacterial Agents↗
PubMed2001

A structural approach into human tryptophan hydroxylase and its implications for the regulation of serotonin biosynthesis.

Tryptophan hydroxylase (TPH) catalyzes the 5-hydroxylation of tryptophan, which is the first step in the biosynthesis of indoleamines (serotonin and melatonin). Serotonin functions mainly as a neurotransmitter, whereas melatonin is the principal hormone secreted by the pineal gland. TPH belongs to the family of the aromatic amino acid hydroxylases, including phenylalanine hydroxylase (PAH) and tyrosine hydroxylase (TH), which all have a strict requirement for dioxygen, non-heme iron (II) and tetrahydrobiopterin (BH4). During the last three years there has been a formidable increase in the amount of structural information about PAH and TH, which has provided new insights into the active site structure, the binding of substrates, inhibitors and pterins, as well as on the effect of disease-causing mutations in these hydroxylases. Although structural information about TPH is not yet available, the high sequence homology between the three mammalian hydroxylases, notably at the catalytic domains, and the similarity of the reactions that they catalyze, indicate that they share a similar 3D-structure and a common catalytic mechanism. Thus, we have prepared a model of the structure of TPH based on the crystal structures of TH and PAH. This structural model provides a frame for understanding the specific interactions of TPH with L-tryptophan and substrate analogues, BH4 and cofactor analogues, L-DOPA and catecholamines. The interactions of these ligands with the enzyme are discussed focusing on the physiological and pharmacological regulation of serotonin biosynthesis, notably by tryptophan supplementation therapy and substitution therapy with tetrahydrobiopterin analogues (positive effects), as well as the effect of catecholamines on TPH activity in L-DOPA treated Parkinson's disease patients (enzyme inhibition).

Amino Acid Sequence↗
PubMed2000

Cyclooxygenase-2 expression is abundant in alveolar type II cells in lung cancer-sensitive mouse strains and in premalignant lesions.

Overexpression of cyclooxygenase-2 (COX-2) is seen in a high percentage of human colon tumors, lung adenocarcinomas and other cancers. Inhibition of this enzyme represses human colon tumorigenesis and decreases lung tumor multiplicity in 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-exposed A/J mice. The purpose of this investigation was to characterize the expression of cyclooxygenase-2 (COX-2) during tumor progression in the A/J mouse lung and to compare the results with expression in other cancer-susceptible and several cancer-resistant mouse strains. Analysis of normal A/J mouse lung showed that type II alveolar epithelial cells express high levels of COX-2 protein and mRNA, indicating that COX-2 is present constitutively in this tumor progenitor cell prior to any carcinogen exposure. Examination of lung-cancer-resistant (C3H/HeJ, C57BL/6J, DBA/2J) and other lung-cancer-susceptible (A/WySnJ, SWR/J) strains showed similar levels of COX-2 mRNA expression in the three susceptible strains and lower levels of expression in two of the resistant strains, indicating a possible correlation between COX-2 expression in type II cells and lung cancer susceptibility. COX-2 protein expression was observed in A/J lung tumors at all stages of development. Variation and occasional absence of protein expression were also observed in A/J lung tumors, particularly in adenomas and adenocarcinomas, suggesting that COX-2 is not obligatory for maintenance of the malignant phenotype. In support of this conclusion, treatment of xenografted cell lines derived from malignant murine pulmonary tumors with COX-2 inhibitors produced only a slight repression of growth. However, the frequent expression of COX-2 in early lesions in the A/J mouse lung combined with the known reduction in tumor number in animals treated with COX-2 inhibitors prior to carcinogen exposure indicate that COX-2 could be a promising target for lung cancer chemoprevention. In addition, high levels of COX-2 expression in the normal tumor-progenitor cells of lung-cancer-sensitive mice indicate that COX-2 may play a role in lung cancer susceptibility.

Animals↗
PubMed1975

[Natural history of molecular pathology].

The author recalls the main stages of biosynthesis of proteins based on molecular pathology : transcription of DNA into messenger RNA, the genetic code, translation of protein molecules and regulation of their synthesis. Examples are then given of qualitative and quantitative disturbances. Qualitative disturbances with synthesis of abnormal proteins, or protein diseases of protein structure, together with their consequences. Quantitative disorders, with modified synthesis of normal proteins, result very often from abnormalities of structural genes, but also from abnormalities of transcription or translation. The author considers, in conclusion, pathological situations based on molecular abnormalities for mutations occur at random and it may be possible to correct them by genetic manipulation.

Amino Acid Sequence↗
PubMedDate not supplied

[Determination of the rate constants for the interaction of enzymes with substrates and inhibitors during a short incubation time].

Kinetics of enzymatic reactions was studied using equipment which permitted to decrease the time of incubation of an enzyme with substrate or inhibitor up to two sec; principles of action, design and experimental procedure are described. A method of pipetting under pressure was employed to accelerate an addition of suitable reagents to the enzyme solution and for rapid stirring of the reaction mixture. Time of incubation was automatically measured with a precision of plus or minus 0.01 sec using an electronic stop-watch. Start and stop of the watch were made by means of electric gauges with platinum electrodes, placed into the channels through which the substrate or inhibitor solutions were supplied to the reaction mixture.

Cholinesterase Inhibitors↗