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Biomedical subjects

B J Wallace

Publications and source records attributed to B J Wallace.

At least 37 records · Page 2Linked to original sources
PubMed1978

Streptomycin causes misreading of natural messenger by interacting with ribosomes after initiation.

The induction of misreading by streptomycin in vitro, previously observed with synthetic messengers, is now demonstrated with natural (endogenous or viral) messenger by the use of extracts of temperature sensitive mutants lacking Glu--tRNA or Val--tRNA synthetase. With chain-elongating but noninitiating ribosomes (i.e., purified polysomes) deprived of an aminoacyl--tRNA, streptomycin and other aminoglycosides, over a wide range of concentrations, stimulate incorporation. With ribosomes initiating in the presence of streptomycin stimulation is also observed but it is restricted, just like phenotypic suppression in cells, to very low streptomycin concentrattions which evidently allow some ribosomes to initiate and later encounter them in the course of chain elongation. The stimulation is accompanied by an increase in the size of the products; hence, it is evidently due to substitution of an incorrect aminoacyl--tRNA for a missing one. The test introduced here also has revealed a misreading effect of streptomycin on resistant ribosomes. In addition, significant intrinsic misreading was observed without streptomycin, indicating that under optimal conditions for in vitro protein synthesis an empty codon is frequently read by an incorrect aminoacyl--tRNA.

Anti-Bacterial Agents↗
PubMed1977

Aerobic respiration in mutants of Escherichia coli accumulating quinone analogues of ubiquinone.

The ability of three naturally occurring analogues of ubiquinone to function in aerobic respiration in Escherichia coli has been studied. The compounds, which differ from ubiquinone in terms of the substituents on the quinone ring, accumulate in the cytoplasmic membranes of ubiE-, ubiF- and ubiG- mutants. One of the analogues (2-octaprenyl-3-methyl-6-methoxy-1,4-benzoquinone, NMQ), which lacks the 5-methoxyl group of the benzoquinone ring of ubiquinone promoted the oxidation of NADH, D-lactate and alpha-glycerophosphate but not succinate. Electron transport supported by MMQ was found to be coupled to phosphorylation. In contrast, 2-octaprenyl-6-methoxy-1,4-benzoquinone, which lacks both the 3-methyl and 5-methoxyl groups of ubiquinone, and 2-octaprenyl-3-methyl-5-hydroxy-6-methoxy-1,4-benzoquinone, in which the 5-methoxyl group of ubiquinone is replaced by an hydroxyl group, were virtually inactive in the oxidases tested. The ability of MMQ to function in respiration in isolated membranes is consistent with the findings that the growth rate and yield of a ubiF- strain, unlike other ubi- strains, were only slightly lower than those of a ubiF+ strain. The fact that MMQ is active in some but not all oxidases provides further support for the concept that the quinones link the individual dehydrogenases to the respiratory chain and that each dehydrogenase has specific structural requirements for quinone acceptors.

Aerobiosis↗
PubMed1977

Role of quinones in electron transport to oxygen and nitrate in Escherichia coli. Studies with a ubiA- menA- double quinone mutant.

A ubiA- menA- double quinone mutant of Escherichia coli K12 was constructed together with other isogenic strains lacking either ubiquinone or menaquinone. These strains were used to study the role of quinones in electron transport to oxygen and nitrate. Each of the four oxidases examined (NADH, D-lactate, alpha-glycerophosphate and succinate) required a quinone for activity. Ubiquinone was active in each oxidase system while menaquinone gave full activity in alpha-glycerophosphate oxidase, partial activity in D-lactate oxidase but was inactive in NADH and succinate oxidation. The aerobic growth rates, growth yields and products of glucose metabolism of the quinone-deficient strains were also examined. The growth rate and growth yield of the ubi+menA- strain was the same as the wild-type strain, whereas the ubiA-men+ strain grew more slowly on glucose, had a lower growth yield (30% of wild type) and accumulated relatively large quantities of acetate and lactate. The growth of the ubiA-menA- strain was even more severely affected than that of the ubiA-men+ strain. Electron transport from formate, D-lactate, alpha-glycerophosphate and NADH to nitrate was also highly dependent on the presence of a quinone. Either ubiquinone or menaquinone was active in electron transport from formate and the activity of the quinones in electron transport from the other substrates was the same as for the oxidase systems. In contrast, quinones were not obligatory carriers in the anaerobic formate hydrogenlyase system. It is concluded that the quinones serve to link the various dehydrogenases with the terminal electron transport systems to oxygen and nitrate and that the dehydrogenases possess a degree of selectivity with respect to the quinone acceptors.

Aerobiosis↗
PubMed1976

Mutations affecting the reduced nicotinamide adenine dinucleotide dehydrogenase complex of Escherichia coli.

A strain carrying a point mutation affecting the NADH dehydrogenase complex of Escherichia coli has been isolated and its properties examined. The gene carrying the mutation (designated ndh) was located on the E. coli chromosome at about minute 23 and was shown to be cotransducible with the pyrC gene. Strain carrying the ndh- allele were found to be unable to grow on mannitol and to grow very poorly on glucose unless the medium was supplemented with succinate, acetate or casamino acids. The following properties of strains carrying the ndh- allele were established which suggest that the mutation affects the NADH dehydrogenase complex but apparently not the primary dehydrogenase. Membrane preparations possess normal to elevated levels of D-lactate oxidase and succinate oxidase activities but NADH oxidase is absent. NADH is unable to reduce ubiquinone in the aerobic steady state and reduces cytochrome b very slowly when the membranes become anaerobic. NADH dehydrogenase, measured as NADH-dichlorophenolindophenol reductase is reduced but not absent. NADH oxidase is stimulated by menadione although not by Q-3 or MK-1 and in the presence of menadione, cytochrome b is reduced normally by NADH. Further mutants affected in NADH oxidase were isolated using a screening procedure based on the growth characteristics of the original ndh- strain. The mutantions carried by these strains were all cotransducible with the pyrC gene and the biochemical properties of the additional mutants were similar to those of the original mutant. The properties of the group of ndh- mutants established so far suggest that they are affected in the transfer of reducing equivalents from the NADH dehydrogenase complex to ubiquinone.

Aerobiosis↗
PubMed1974

Selective inhibition of initiating ribosomes by spectinomycin.

Spectinomycin at low concentrations inhibits initiating ribosomes but not ribosomes already engaged in chain elongation. The initiating ribosomes are blocked in some step after formation of the initiation complex, probably the first translocation. Cells inhibited by spectinomycin accumulate polysomes, and these have proved to be unstable polyinitiation complexes: they can be pulse-labeled with methionine but not with valine, and they disappear after addition of rifampicin. Hence, the blocked ribosomes evidently are released and then reinitiate. In heterozygotes this cyclic reinitiation by the sensitive ribosomes, each blocking an initiation site for an average of 10-15 min, can explain (just as with streptomycin) the dominance of sensitivity over resistance.

Bacterial Proteins↗
PubMed1973

Partial inhibition of polysomal ribosomes of Escherichia coli by streptomycin.

With purified initiation-free polysomes of E. coli, whether endogenous or formed in vitro on phage R17 RNA, streptomycin causes partial inhibition of chain elongation. The degree of inhibition is constant over a broad range of streptomycin concentration and decreases markedly with increasing Mg(++) concentration. Hence, streptomycin evidently complexes readily with polysomal ribosomes, causing a partial block in chain elongation. Streptomycin has already been shown to cause a complete block of chain elongation by free ribosomes forming initiation complexes in its presence. The production of a different effect on polysomal ribosomes explains how streptomycin can exert two mutually exclusive effects in cells: phenotypic suppression at low concentrations and irreversible inhibition of protein synthesis at higher concentrations. It also becomes possible to understand why killing by streptomycin is antagonized by agents (such as chloramphenicol) that cause a stable blockade of the ribosomes in polysomes.

Carbon Isotopes↗
PubMed1969

Regulator gene controlling enzymes concerned in tyrosine biosynthesis in Escherichia coli.

Mutants of Escherichia coli K-12 have been isolated in which several enzymes concerned with tyrosine biosynthesis are derepressed. These mutants were obtained from a parent strain possessing only a single 3-deoxy-d-arabinoheptulosonic acid-7-phosphate (DAHP) synthetase isoenzyme, DAHP synthetase (tyr), by selecting for resistance to the tyrosine analogue, 4-aminophenylalanine. The mutation responsible for this derepression has been mapped and the gene, which is not closely linked to aroF and tyrA, has been designated tyrR.

Chromatography↗
PubMed1969

Inhibition of 3-deoxy-d-arabinoheptulosonic acid-7-phosphate synthetase (trp) in Escherichia coli.

The growth of a strain of Escherichia coli K-12 which possesses only the single isoenzyme 3-deoxy-d-arabinoheptulosonic acid-7-phosphate (DAHP) synthetase (trp), and which makes this enzyme constitutively, is inhibited by tryptophan. The accumulation of DAHP by a derivative of this strain unable to convert DAHP to dehydroquinate is also inhibited by tryptophan. The enzymic activity of DAHP synthetase (trp) in the presence of CO(2+) is sensitive to inhibition by tryptophan. Mutant strains of E. coli have been isolated in which DAHP synthetase (trp) is feedback-resistant.

Chromosome Mapping↗
PubMed1969

Regulation of 3-deoxy-D-arabino-heptulosonic 7-phosphate acid synthetase activity in relation to the synthesis of the aromatic vitamins in Escherichia coli K-12.

Both in vivo and in vitro experiments on wild-type Escherichia coli K-12 and mutant strains possessing only single 3-deoxy-d-arabino-heptulosonic 7-phosphate acid (DAHP) synthetase isoenzymes indicated that, under conditions when all three isoenzymes are fully repressed, sufficient chorismate is still formed for the synthesis of aromatic vitamins. Under repressed conditions both DAHP synthetase (phe) and (trp), but not DAHP synthetase (tyr), were shown to contribute to vitamin production.

Aldehyde-Lyases↗
PubMed1967

Genetic and biochemical analysis of the isoenzymes concerned in the first reaction of aromatic biosynthesis in Escherichia coli.

Mutant strains of Escherichia coli K-12 were isolated possessing mutations which affected the tyrosine-inhibitable 3-deoxy-d-arabinoheptulosonic acid-7-phosphate (DAHP) synthetase, the phenylalanine-inhibitable DAHP synthetase, or the tryptophan-repressible DAHP synthetase. The mutations causing the loss of each of these activities have been mapped and are widely separated from each other on the E. coli chromosome. Chromatography on diethylaminoethyl cellulose columns allowed the recognition of four peaks of activity.

Amino Acids↗