Biomedical subjects

D-H Lee

Publications and source records attributed to D-H Lee.

7 recordsLinked to original sources

PubMed2003

Consortium of fold-catalyzing proteins increases soluble expression of cyclohexanone monooxygenase in recombinant Escherichia coli.

The cyclohexanone monooxygenase ( CHMO) gene of Acinetobacter sp. NCIMB 9871 was simultaneously expressed with the genes encoding molecular chaperones and foldases in Escherichia coli. While the expression of the CHMO gene alone resulted in the formation of inclusion bodies, coexpression of the chaperone or foldase genes remarkably increased the production of soluble CHMO enzyme in recombinant E. coli. Furthermore, it was found that molecular chaperones were more beneficial than foldases for enhancing active CHMO enzyme production. The recombinant E. coli strain simultaneously expressing the genes for CHMO, GroEL/GroES and DnaK/DnaJ/GrpE showed a specific CHMO activity of 111 units g(-1) cell protein, corresponding to a 38-fold enhancement in CHMO activity compared with the control E. coli strain expressing the CHMO gene alone.

Acinetobacter↗

PubMed2003

Relating atomic-scale electronic phenomena to wave-like quasiparticle states in superconducting Bi2Sr2CaCu2O8+delta.

The electronic structure of simple crystalline solids can be completely described in terms either of local quantum states in real space (r-space), or of wave-like states defined in momentum-space (k-space). However, in the copper oxide superconductors, neither of these descriptions alone may be sufficient. Indeed, comparisons between r-space and k-space studies of Bi2Sr2CaCu2O8+delta (Bi-2212) reveal numerous unexplained phenomena and apparent contradictions. Here, to explore these issues, we report Fourier transform studies of atomic-scale spatial modulations in the Bi-2212 density of states. When analysed as arising from quasiparticle interference, the modulations yield elements of the Fermi-surface and energy gap in agreement with photoemission experiments. The consistency of numerous sets of dispersing modulations with the quasiparticle interference model shows that no additional order parameter is required. We also explore the momentum-space structure of the unoccupied states that are inaccessible to photoemission, and find strong similarities to the structure of the occupied states. The copper oxide quasiparticles therefore apparently exhibit particle-hole mixing similar to that of conventional superconductors. Near the energy gap maximum, the modulations become intense, commensurate with the crystal, and bounded by nanometre-scale domains. Scattering of the antinodal quasiparticles is therefore strongly influenced by nanometre-scale disorder.

Journal Article↗

PubMed2003

Comparative analysis of superfamilies of NBS-encoding disease resistance gene analogs in cultivated and wild apple species.

Eleven distinct families of resistance gene analogs (RGAs) with the characteristic nucleotide-binding sequence (NBS) were identified in two wild apple species, Malus prunifolia and M. baccata, and two cultivated apple cultivars, M. domestica cv. Fuji and M. domestica cv. Hong-ok, using PCR approaches with degenerate primers based on two conserved motifs of known NBS-LRR resistance genes. These RGA families were found to be represented in all the apple species tested, including wild and cultivated species. However, their sequences are very divergent from each other. Furthermore, the low level of recombination detected within their RGA families supports the idea that the evolution of NBS-encoding sequences in apple species involves the gradual accumulation of mutations. Despite the high diversity of the RGA families found in all apple species, the apparent lack of differentiation between wild and cultivated forms suggests that other factors, such as the capacity to tolerate pathogens, might play an important role in the survival of wild-type species.

Amino Acid Sequence↗

PubMed2003

Gamma-glutamyltransferase and diabetes--a 4 year follow-up study.

AIMS/HYPOTHESIS: Gamma-glutamyltransferase (GGT) is located on the external surface of most cells and mediates the uptake of gluthathione, an important component of intracellular antioxidant defenses. An increase in GGT concentration has been regarded as a marker of alcohol consumption or liver disease. However, more subtle gradations in GGT could be informative because its expression is enhanced by oxidative stress and it could be released by several conditions inducing cellular stress. Recently, serum GGT concentrations have been associated with many cardiovascular disease risk factors or components of the insulin resistance syndrome. We did a prospective study with the hypothesis that serum GGT is a predictor of incident diabetes. METHODS: A total of 4,088 healthy men working in a steel manufacturing company were examined in 1994 and 1998. Diabetes was defined as a serum fasting glucose concentration of more than 126 mg/dl or the use of diabetes medication. RESULTS: There was a strong dose-response relation between serum GGT concentrations at baseline and the incidence of diabetes. In contrast to the 31% of men with GGT concentrations under 9 U/l, adjusted relative risks for incidence of diabetes for GGT concentrations 10-19, 20-29, 30-39, 40-49, and over 50 U/l were 8.0, 13.3, 12.6, 19.6 and 25.8, respectively. The associations of age and BMI with incident diabetes became stronger the higher the value of baseline serum GGT concentration. CONCLUSION/INTERPRETATION: This study suggests that an increase in GGT concentration within its physiological range is a sensitive and early biomarker for the development of diabetes.

Adult↗

PubMed2003

Duality relation for frustrated spin models.

We consider discrete spin models on arbitrary planar graphs and lattices with frustrated interactions. We first analyze the Ising model with frustrated plaquettes. We use an algebraic approach to derive the result that an Ising model with some of its plaquettes frustrated has a dual model which is an Ising model with an external field ipi/2 applied to the dual sites centered at frustrated plaquettes. In the case where all plaquettes are frustrated, this leads to the known result that the dual model has a uniform field ipi/2, whose partition function can be evaluated in the thermodynamic limit for regular lattices. The analysis is extended to a Potts spin glass with analogous results obtained.

Journal Article↗

PubMed2002

PAH utilization by Pseudomonas rhodesiae KK1 isolated from a former manufactured-gas plant site.

Pseudomonas rhodesiae KK1 was isolated from a former manufactured-gas plant site, due to its ability to grow rapidly in a mixture of polycyclic aromatic hydrocarbons (PAHs). Radiorespirometric analysis revealed that strain KK1 was found to be able to mineralize anthracene, naphthalene and phenanthrene. Notably, phenanthrene-grown cells were able to mineralize anthracene much more rapidly than naphthalene-grown cells. Comparative analysis of amino acid sequences from 17 randomly selected dioxygenases capable of hydroxylating unactivated aromatic nuclei indicated that the enzymes for catabolism of PAHs, such as naphthalene and phenanthrene, might exist redundantly in strain KK1. Northern hybridization for cells grown on naphthalene or phenanthrene, using the putative naphthalene or phenanthrene dioxygenase gene fragment as a probe, suggested that the enzyme for naphthalene catabolism might share some homology in deduced amino acid sequences with phenanthrene dioxygenases. Also, it was found that three lipids (17:0 cyclo, 18:1 omega7c, 19:0 cyclo) increased in response to both naphthalene and phenanthrene, while the shift of other lipids varied from substrate to substrate.

Anthracenes↗

PubMed2002

Imaging quasiparticle interference in Bi2Sr2CaCu2O8+delta.

Scanning tunneling spectroscopy of the high-Tc superconductor Bi2Sr2CaCu2O8+delta reveals weak, incommensurate, spatial modulations in the tunneling conductance. Images of these energy-dependent modulations are Fourier analyzed to yield the dispersion of their wavevectors. Comparison of the dispersions with photoemission spectroscopy data indicates that quasiparticle interference, due to elastic scattering between characteristic regions of momentum-space, provides a consistent explanation for the conductance modulations, without appeal to another order parameter. These results refocus attention on quasiparticle scattering processes as potential explanations for other incommensurate phenomena in the cuprates. The momentum-resolved tunneling spectroscopy demonstrated here also provides a new technique with which to study quasiparticles in correlated materials.

Journal Article↗