Understanding the bulk electronic structure of Ca1-xSrxVO3

We investigate the electronic structure of Ca1-xSrxVO3 using careful state-of-the-art experiments and calculations. Photoemission spectra using synchrotron radiation reveal a hitherto unnoticed polarization dependence of the photoemission matrix elements for the surface component leading to a substantial suppression of its intensity. Bulk spectra extracted with the help of experimentally determined electron escape depth and estimated suppression of surface contributions resolve outstanding puzzles concerning the electronic structure in Ca1-xSrxVO3.Comment: 4 pages including 3 figure

Uridine-diphosphate-glucose 4-epimerase from saccharomyces fragilis: inactivation by heat and reconstitution of the inactive enzyme

UDP-glucose 4-epimerase from Saccharamyces fragilis is rapidly inactivated by heating at 42 °C for 7 min and at 45 °C for 4 min. The effector site. specific for sugar phosphates, is destroyed still earlier. The enzyme is inactivated by the dissociation of NAD from it leaving the dimeric structure unaffected. It call be reactivated by mercaptoetlianol and NAD, both of which are essential for reactivation, and NAD becomes associated with the dimeric protein moiety

Molecular association of glucose-6- phosphate isomerase and pyruvate kinase M2 with glyceraldehyde-3-phosphate dehydrogenase in cancer cells

Background: For a long time cancer cells are known for increased uptake of glucose and its metabolization through glycolysis. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a key regulatory enzyme of this pathway and can produce ATP through oxidative level of phosphorylation. Previously, we reported that GAPDH purified from a variety of malignant tissues, but not from normal tissues, was strongly inactivated by a normal metabolite, methylglyoxal (MG).Molecular mechanism behind MG mediated GAPDH inhibition in cancer cells is not well understood. Methods: GAPDH was purified from Ehrlich ascites carcinoma (EAC) cells based on its enzymatic activity. GAPDH associated proteins in EAC cells and 3-methylcholanthrene (3MC) induced mouse tumor tissue were detected by mass spectrometry analysis and immunoprecipitation (IP) experiment, respectively. Interacting domains of GAPDH and its associated proteins were assessed by in silico molecular docking analysis. Mechanism of MG mediated GAPDH inactivation in cancer cells was evaluated by measuring enzyme activity, Circular dichroism (CD) spectroscopy, IP and mass spectrometry analyses. Result: Here, we report that GAPDH is associated with glucose-6-phosphate isomerase (GPI) and pyruvate kinase M2 (PKM2) in Ehrlich ascites carcinoma (EAC) cells and also in 3-methylcholanthrene (3MC) induced mouse tumor tissue. Molecular docking analyses suggest C-terminal domain preference for the interaction between GAPDH and GPI. However, both C and N termini of PKM2 might be interacting with the C terminal domain of GAPDH. Expression of both PKM2 and GPI is increased in 3MC induced tumor compared with the normal tissue. In presence of 1 mM MG,association of GAPDH with PKM2 or GPI is not perturbed, but the enzymatic activity of GAPDH is reduced to 26.8 ± 5 % in 3MC induced tumor and 57.8 ± 2.3 % in EAC cells. Treatment of MG to purified GAPDH complex leads to glycation at R399 residue of PKM2 only, and changes the secondary structure of the protein complex. Conclusion: PKM2 may regulate the enzymatic activity of GAPDH. Increased enzymatic activity of GAPDH in tumor cells may be attributed to its association with PKM2 and GPI. Association of GAPDH with PKM2 and GPI could be a signature for cancer cells. Glycation at R399 of PKM2 and changes in the secondary structure of GAPDH complex could be one of the mechanisms by which GAPDH activity is inhibited in tumor cells by MG

A microspectroscopic study of the electronic homogeneity of ordered and disordered Sr2FeMoO6

Besides a drastic reduction in saturation magnetization of disordered Sr2FeMoO6 compared to highly ordered samples, magnetizations as a function of the temperature for different disordered samples may also show qualitatively different behaviors. We investigate the origin of such diversity by performing spatially resolved photoemission spectroscopy on various disordered samples. Our results establish that extensive electronic inhomogeneity, arising most probably from an underlying chemical inhomogeneity in disordered samples is responsible for the observed magnetic inhomogeneity. It is further pointed out that these inhomogeneities are connected with composition fluctuations of the type Sr2Fe1+xMo1-xO6 with Fe-rich (x>0) and Mo-rich (x<0) regions.Comment: 14 pages, 4 figure

Udpglucose-4 epimerase from Saccharomyces fragilis: interaction with sugar phosphates at an effector site

UDP glucose-4 epimerase from Saccharomyces fragilis was found to be activated at low substrate concentrations by some metabolically related sugar phosphates. The stimulation of the enzyme activity showed a sigmoidal response to the increasing concentration of glucose-6 phosphate at a fixed substrate concentration. The activated enzyme was allosterically inhibited by UMP which otherwise acted as a strictly competitive inhibitor for the enzyme. The interaction with sugar phosphates was not accompanied by any change in the aggregation state of the molelcule

Udpglucose 4-epimerase from saccharomyces fragilis : desensitization with heat

The allosteric kinetics exhibited by UDP glucose 4-epimerase from Saccharomyces fragilis changes over to a normal hyperbolic kinetics when the enzyme is heated at 41° for 2 mins. The native enzyme is completely insensitive to inhibition by UMP in the allosteric region. The desensitized enzyme is however, strongly inhibited by UMP at this low concentrations. Apparently, desensitization by heat converts the enzyme to its ultimate catalytic form