Search PubMed⌕ Search

Biomedical subjects

E B Newman

Publications and source records attributed to E B Newman.

At least 37 records · Page 2Linked to original sources
PubMed1990

A possible mechanism for the in vitro activation of L-serine deaminase activity in Escherichia coli K12.

L-Serine deaminase is inactive in crude extracts of Escherichia coli K12, but can be activated by incubation with iron and dithiothreitol. This activation requires oxygen, and is inhibited by free radical scavengers and by diethylene triamine pentaacetic acid, which prevents Fe cycling. We suggest that in vitro activation of L-serine deaminase is catalyzed by an oxidant (perhaps hydroxyl radicals). Also, activation may be accompanied by a decrease in molecular weight and involve both a cleavage of the polypeptide chain and a reversible reduction of the molecule.

Antioxidants↗
PubMed1989

L-serine degradation in Escherichia coli K-12: cloning and sequencing of the sdaA gene.

A new mutant of Escherichia coli K-12 unable to grow with L-serine, glycine, and L-leucine has been isolated by lambda plac Mu insertion and shown to be deficient in L-serine deaminase activity. The corresponding gene, sdaA, has been cloned from a prototrophic strain, and the clone has been characterized and sequenced. The evidence is consistent with the hypothesis that sdaA is the structural gene for L-serine deaminase. However, other possibilities are also considered. No significant homology with previously reported DNA or protein sequences was detected.

Amino Acid Sequence↗
PubMed1988

A deficiency in cyclic AMP results in pH-sensitive growth of Escherichia coli K-12.

Mutants of Escherichia coli K-12 deficient in adenyl cyclase (cya) and catabolite activator protein (crp) have been shown to grow more slowly than their parent strains in glucose-minimal medium. Their growth rate decreased markedly with increasing pH between 6 and 7.8. We have shown that this pH sensitivity is a direct consequence of the cya mutation, because a mutation to pH resistance also restored ability to ferment a variety of sugars. The proton motive force-dependent uptake of proline and glutamate was also reduced and sensitive to pH in the cya mutant. The membrane-bound ATPase activity was normal. The rate of oxygen uptake by cells, although reduced, was pH insensitive. We suggest several explanations for this phenotype, including a possible defect in energy transduction.

Adenylyl Cyclases↗
PubMed1986

An estimate of the extent of deamination of L-serine in auxotrophs of Escherichia coli K-12.

We have shown that serine-glycine auxotrophs of Escherichia coli K-12 use exogenous L-serine inefficiently as a source of biosynthetic intermediates. Much of the L-serine supplied in the medium is not used to satisfy the auxotrophic requirement, owing to its diversion by L-serine deaminase, presumably to pyruvate. This is the first proof that the activity known as L-serine deaminase actually deaminates L-serine in vivo.

Culture Media↗
PubMed1985

A mutation in Escherichia coli K-12 results in a requirement for thiamine and a decrease in L-serine deaminase activity.

Mutants of Escherichia coli K-12 deficient in L-serine deaminase (L-SD) activity have been isolated. These strains required thiamine and grew normally when it was provided. The decrease in L-SD activity caused no obvious metabolic deficiency. A study of revertants and transductants showed that a single mutation was responsible for the thiamine requirement and for the decrease in L-SD activity.

Drug Resistance, Microbial↗
PubMed1985

In vitro and in vivo activation of L-serine deaminase in Escherichia coli K-12.

Escherichia coli L-serine deaminase (L-SD) in crude extracts made in glycylglycine could be activated by incubation with iron sulfate and dithiothreitol. This activation could also be demonstrated in vitro in two mutants which were physiologically deficient in L-SD activity in vivo. This suggests that these mutants were deficient not in L-SD but in an enzyme(s) activating L-SD. The suggestion is made that production of a functional L-SD in vivo requires activation of the structural gene product by an enzyme or enzymes that reduce the protein to an active form.

Buffers↗
PubMed1982

L-serine degradation in Escherichia coli K-12: directly isolated ssd mutants and their intragenic revertants.

Two methods for the direct isolation of spontaneous ssd mutants of Escherichia coli K-12 strains are described; (i) by growth with L-serine as the carbon source, and (ii) by low-level kanamycin resistance. A newly isolated mutant had the same phenotype as the mutant described previously, including inefficient use of the glucose, inability to growth with succinate, altered transport characteristics, and altered resistance to certain growth effectors. Succinate-utilizing derivatives which appear to be intragenic are characterized in detail. The relation between the mutants isolated here and mutants which are thought to have impairment in a system of coupling respiratory energy to active transport (ecfB mutants) is discussed.

Biological Transport, Active↗
PubMed1982

L-serine degradation in Escherichia coli K-12: a combination of L-serine, glycine, and leucine used as a source of carbon.

Escherichia coli K-12 strain CU1008 cannot use L-serine as the sole carbon source, but it could use L-serine as an auxiliary carbon source with glucose, L-alanine, or pyruvate and could derive energy from L-serine to support oxygen uptake. CU1008 grew with L-serine if it was also provided with glycine and leucine. These may act by increasing the available activity of L-serine deaminase; other explanations are also explored.

Energy Metabolism↗
PubMed1982

L-Serine deaminase activity is induced by exposure of Escherichia coli K-12 to DNA-damaging agents.

The synthesis of L-serine deaminase in Escherichia coli K-12 was induced after exposure of cells to a variety of DNA-damaging agents, including UV irradiation, nalidixic acid, and mitomycin C. Synthesis was also induced during growth at high temperature. A mutant constitutive for SOS functions showed an elevated level of L-serine deaminase activity. The response to DNA-damaging agents thus may be mediated via the SOS system.

Antibiotics, Antineoplastic↗
PubMed1982

Control of nitrogenase in a photosynthetic autotrophic bacterium, Ectothiorhodospira sp.

An Ectothiorhodospira species fixed nitrogen when grown as an autotroph in completely inorganic medium by using a variety of electron donors. The organism also used organic carbon sources; however, this required induction of synthesis of various enzymes, whereas the enzymes needed for autotrophic growth were synthesized constitutively. Nitrogenase induction and function were inhibited by ammonium chloride. Nitrogenase activity was dependent on light and inhibited by oxygen.

Aerobiosis↗
PubMed1981

A mutation affecting L-serine and energy metabolism in E. coli K12.

The effects of a pleiotropic mutation ssd are described. This mutation results in decreased efficiency in the use of glucose and fructose as carbon source, inability to use succinate or to grow anaerobically, an alteration in the activity of enzymes responsible for the synthesis and degradation of L-serine, increased resistance to certain antibiotics, and a deficiency in proline transport. This mutation resembles various previously described mutations thought to affect' energy coupling factor' and is located in the same region of the chromosome. While the gene product affected by this mutation is still unidentified, it is clear that L-serine metabolism cannot be understood merely in terms of providing L-serine and its derivatives.

Anaerobiosis↗
PubMed1981

Threonine as a carbon source for Escherichia coli.

Threonine can be used aerobically as the sole source of carbon and energy by mutants of Escherichia coli K-12. The pathway used involves the conversion of threonine via threonine dehydrogenase to aminoketobutyric acid, which is further metabolized by aminoketobutyric acid ligase, forming acetyl coenzyme A and glycine. A strain devoid of serine transhydroxymethylase uses this pathway and excretes glycine as a waste product. Aminoketobutyric acid ligase activity was demonstrated after passage of crude extracts through Sephadex G100.

Acetates↗
PubMed1980

Map location of the ssd mutation in Escherichia coli K-12.

A pleiotropic mutation at the ssd locus was mapped at 86 min near rha. A mutation at the ssd locus resulted in elevated L-serine deaminase activity, inability to grow with succinate as the carbon source, and inability to grow anaerobic conditions.

Chromosome Mapping↗
PubMed1980

In vitro studies on L-serine deaminase activity of Escherichia coli K12.

Extracts of Escherichia coli K12 contain an enzyme which deaminates L-serine. This serine deaminase appears to be a soluble enzyme and is inhibited by substrate analogues, metal ions, and chelators. The activity, which is very unstable in vitro, is protected, and in some cases, even activated by substrate, substrate analogues, and by ferrous ion. The enzyme has proved unstable in all attempts at purification. It resembles closely the L-serine deaminase activity in other microorganisms, but is very different from the mammalian enzyme. As judged by comparison with organisms in which this enzyme serves as part of the principal carbon-handling pathway, L-serine deaminase activity is present in E. coli extracts in physiologically significant amounts.

Escherichia coli↗
PubMed1978

A single mutation affects L-serine deaminase, L-leucyl-, L-phenylalanyl-tRNA protein transferase, and proline oxidase activity in Escherichia coli K-12.

A mutation at a single locus, wyb, results in several phenotypic changes in Escherichia coli K-12. The Wyb- phenotype includes: (i) an increase in L-serine deaminase activity, together with a loss of inducibility by L-leucine; (ii) an absence of L-leucyl-, L-phenylalanyl-tRNA protein transferase activity; (iii) inducibility of proline oxidase by proline; and (iv) a loss of ability to use maltose as a carbon and energy source.

Acyltransferases↗
PubMed1978

Factors influencing the in vivo stability of L-serine deaminase activity in E. coli K12.

L-Serine deaminase (L-SD) is unstable in intact cells of Escherichia coli K12. The extent of this instability is dependent on the nitrogen content of the medium in which the enzyme is synthesized, and on that in which it is tested. Enzyme activity in cells grown with an inorganic nitrogen source is unstable in the presence of inorganic nitrogen; enzyme activity in cells grown with an organic nitrogen source is unstable in the presence of the amino acids glycine and leucine.

Ammonium Sulfate↗