3,512 research outputs found
Molecular basis of carbohydrate-deficient glycoprotein syndromes type I with normal phosphomannomutase activity
AbstractCarbohydrate deficient glycoprotein syndromes (CDGS) are inherited disorders in glycosylation. Isoelectric focusing of serum transferrin is used as a biochemical indicator of CDGS; however, this technique cannot diagnose the molecular defect. Even though phosphomannomutase (PMM) deficiency accounts for the great majority of known CDGS cases (CDGS type Ia), newly discovered cases have significantly different clinical presentations than the PMM-deficient patients. These differences arise from other defects affecting the biosynthesis of N-linked oligosaccharides in the endoplasmic reticulum and in the Golgi compartment. The most notable is the loss of phosphomannose isomerase (PMI) (CDGS type Ib). It causes severe hypoglycemia, protein-losing enteropathy, vomiting, diarrhea, and congenital hepatic fibrosis. In contrast to PMM-deficiency, there is no developmental delay nor neuropathy. Most symptoms in the PMI-deficient patients can be successfully treated with dietary mannose supplements. Another defect is the lack of glucosylation of the lipid-linked oligosaccharide precursor. The clinical features of this form of CDGS are milder, but similar to, PMM-deficient patients. Yeast genetic and biochemical techniques were critical in unraveling these disorders since many of the defective genes were known in yeast and corresponding mutants were available for complementation. Yeast strains carrying mutations in the homologous genes are likely to provide conclusive identification of the primary defects in novel CDGS types that affect the synthesis and transfer of precursor oligosaccharides
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Expression of the DNA mismatch repair proteins hMLH1 and hPMS2 in normal human tissues.
hMLH1 and hPMS2 are part of the DNA mismatch repair complex. Mutations in these genes have been linked to hereditary non-polyposis colon cancer; they also occur in a variety of sporadic cancers. Western blot analysis and immunohistochemistry demonstrated that hMLH1 and hPMS2 are widely expressed nuclear proteins with a distribution pattern very similar to that previously described for hMSH2. These observations showing similar localization of hMLH1 and hPMS2 with hMSH2 are consistent with the biochemical function of these proteins in DNA mismatch repair
Fermi surface induced lattice distortion in NbTe
The origin of the monoclinic distortion and domain formation in the quasi
two-dimensional layer compound NbTe is investigated. Angle-resolved
photoemission shows that the Fermi surface is pseudogapped over large portions
of the Brillouin zone. Ab initio calculation of the electron and phonon
bandstructure as well as the static RPA susceptibility lead us to conclude that
Fermi surface nesting and electron-phonon coupling play a key role in the
lowering of the crystal symmetry and in the formation of the charge density
wave phase
Exciton condensation driving the periodic lattice distortion of 1T-TiSe2
We address the lattice instability of 1T-TiSe2 in the framework of the
exciton condensate phase. We show that, at low temperature, condensed excitons
influence the lattice through electron-phonon interaction. It is found that at
zero temperature, in the exciton condensate phase of 1T-TiSe2, this exciton
condensate exerts a force on the lattice generating ionic displacements
comparable in amplitude to what is measured in experiment. This is thus the
first quantitative estimation of the amplitude of the periodic lattice
distortion observed in 1T-TiSe2 as a consequence of the exciton condensate
phase.Comment: 5 pages, 3 figures and 1 tabl
Hot Spots on the Fermi Surface of Bi2212: Stripes versus Superstructure
In a recent paper Saini et al. have reported evidence for a pseudogap around
(pi,0) at room temperature in the optimally doped superconductor Bi2212. This
result is in contradiction with previous ARPES measurements. Furthermore they
observed at certain points on the Fermi surface hot spots of high spectral
intensity which they relate to the existence of stripes in the CuO planes. They
also claim to have identified a new electronic band along Gamma-M1 whose one
dimensional character provides further evidence for stripes. We demonstrate in
this Comment that all the measured features can be simply understood by
correctly considering the superstructure (umklapp) and shadow bands which occur
in Bi2212.Comment: 1 page, revtex, 1 encapsulated postscript figure (color
Spontaneous exciton condensation in 1T-TiSe2: a BCS-like approach
Recently strong evidence has been found in favor of a BCS-like condensation
of excitons in 1\textit{T}-TiSe. Theoretical photoemission intensity maps
have been generated by the spectral function calculated within the excitonic
condensate phase model and set against experimental angle-resolved
photoemission spectroscopy data. Here, the calculations in the framework of
this model are presented in detail. They represent an extension of the original
excitonic insulator phase model of J\'erome \textit{et al.} [Phys. Rev. {\bf
158}, 462 (1967)] to three dimensional and anisotropic band dispersions. A
detailed analysis of its properties and further comparison with experiment are
also discussedComment: Submitted to PRB, 11 pages, 7 figure
Hole Pockets in the Doped 2D Hubbard Model
The electronic momentum distribution of the two
dimensional Hubbard model is studied for different values of the coupling , electronic density , and temperature, using
quantum Monte Carlo techniques. A detailed analysis of the data on
clusters shows that features consistent with hole pockets at momenta appear as the system is doped away
from half-filling. Our results are consistent with recent experimental data for
the cuprates discussed by Aebi et al. (Phys. Rev. Lett. {\bf 72}, 2757 (1994)).
In the range of couplings studied, the depth of the pockets is maximum at , and it increases with decreasing temperature.
The apparent absence of hole pockets in previous numerical studies of this
model is explained.Comment: 11 pages, 4 postscript figures appended, RevTeX (version 3.0
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