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At least 199 records · Page 11Linked to original sources
PubMed1998

Biodegradation of dimethylterephthalate by Comamonas acidovorans D-4.

Comamonas acidovorans D-4, capable of utilizing dimethylterephthalate (DMT) as the sole carbon source, was isolated from the activated sludge of petrochemical wastewater treatment plant. Almost complete utilization of as high as 0.5% (w/v) DMT was observed in 72 hr. Growth kinetics followed a parallel relation between the growth, DMT utilization and cell associated esterase activity. A cell free broth of DMT grown cells showed an extracellular esterase activity. During the DMT degradation an extracellular accumulation of terephthalic acid was found. Although, C. acidovorans grew on a number of phthalate esters and phthalic acids as the sole carbon source, growth was significantly high on phthalic acids. The potential of this organism in petrochemical pollution abatement is discussed.

Biodegradation, Environmental↗
PubMed2001

Characterization of hybrid biphenyl dioxygenases obtained by recombining Burkholderia sp. strain LB400 bphA with the homologous gene of Comamonas testosteroni B-356.

The bacterial degradation of polychlorinated biphenyls depends on the ability of the enzyme biphenyl 2,3-dioxygenase (BPDO) to catalyze their oxygenation. Analysis of hybrid BPDOs obtained using common restriction sites to exchange large DNA fragments between LB400 bphA and B-356 bphA showed that the C-terminal portion of LB400 alpha subunit can withstand extensive structural modifications, and that these modifications can change the catalytic properties of the enzyme. On the other hand, exchanging the C-terminal portion of B-356 BPDO alpha subunit with that of LB400 alpha subunit generated inactive chimeras. Data encourage an enzyme engineering approach, consisting of introducing extensive modifications of the C-terminal portion of LB400 bphA to extend BPDO catalytic properties toward polychlorinated biphenyls.

Burkholderia↗
PubMed1997

Diversity within bacterial isolates hybridizing with Comamonas probe ppT.

Diversity within bacteria isolated from activated sludge and the Baltic sea and recognized by the rRNA targeted oligonucleotide probe ppT (designed by BRAUN-HOWLAND et al., 1993 to recognize C. testosteroni) was studied. The partial nucleotide sequences of 16S genes of the isolates revealed that the activated sludge and Baltic sea isolates each formed a separate group distinct from C. testosteroni. The analysis of phage and bacteriocin sensitivity as well as whole cell protein patterns revealed the same grouping, but in these characters also intragroup variation was observed. As a conclusion, neither of the studied groups were C. testosteroni, but they probably belong to two previously unknown species common in activated sludge or the Baltic sea.

Bacterial Proteins↗
PubMed1994

Mechanism of the reaction catalyzed by delta 5-3-ketosteroid isomerase of Comamonas (Pseudomonas) testosteroni: kinetic properties of a modified enzyme in which tyrosine 14 is replaced by 3-fluorotyrosine.

Tyrosine 14 of delta 5-3-ketosteroid isomerase plays an important role in the function of the enzyme, since its replacement by phenylalanine results in a decrease in kcat by a factor of 10(-4.7). This result and the fact that this residue resides in the enzyme's substrate binding site and is in close proximity to C-2 of the bound steroid suggests that it functions as an electrophile in the catalytic mechanism by protonation of or hydrogen bonding to the C-3 carbonyl oxygen of the substrate. In order to obtain more information about the role of tyrosine 14, we have prepared a modified form of the enzyme in which tyrosine 14 has been substantially replaced in vivo by exogenously supplied 3-fluorotyrosine, a tyrosine derivative in which the pKa' of the phenol hydroxyl should be decreased by about 1.5 log units. Site specificity of this modification has been ensured by mutation of the codons for the nonessential tyrosines 55 and 88 to phenylalanine. We find that replacement of tyrosine 14 by 3-fluorotyrosine in the Y55,88F modified form of the isomerase results in a 4-fold decrease in kcat. We interpret this result in terms of a mechanism in which the transition state for enolization is dienolate-like, characterized by relatively little proton transfer from tyrosine 14 in the transition state, and the intermediate in the overall reaction is dienol-like. An alternative mechanism in which the intermediate is stabilized by a short, strong hydrogen bond can also be consistent with the data.

Base Sequence↗
PubMed1998

High-efficiency incorporation in vivo of tyrosine analogues with altered hydroxyl acidity in place of the catalytic tyrosine-14 of Delta 5-3-ketosteroid isomerase of Comamonas (Pseudomonas) testosteroni: effects of the modifications on isomerase kinetics.

Versions of the Y55F/Y88F modified form of Delta 5-3-ketosteroid isomerase in which the active-site tyrosine-14 is replaced by 2-fluorotyrosine, 3-fluorotyrosine, and 2,3-difluorotyrosine, amino acids having progressively greater acidity of their phenolic hydroxyls, have been expressed in an Escherichia coli host and purified to high homogeneity. The steady-state kinetic properties of Y55F/Y88F KSI and its fluorotyrosine modified forms have been determined. The mechanistic implications of the results are presented and discussed.

Amino Acid Substitution↗