Vitamin B(6) salvage enzymes: mechanism, structure and regulation. (17/43)


Rv2607 from Mycobacterium tuberculosis is a pyridoxine 5'-phosphate oxidase with unusual substrate specificity. (18/43)


Proteomics analysis of gastric epithelial AGS cells infected with Epstein-Barr virus. (19/43)

Effects of the Epstein-Barr virus (EBV) on cellular protein expression are essential for viral pathogenesis. To characterize the cellular response to EBV infection, differential proteomes of gastric epithelial AGS cells were analyzed with two-dimensional gel electrophoresis (2-DE) followed by matrix-assisted laser desorption/ionization- time of flight (MALDI-TOF) and liquid chromatography electrospray/ionization ion trap (LC-ESI-IT) mass spectrometry identification. Mass spectrometry identified 9 altered cellular proteins, including 5 up-regulated and 4 down-regulated proteins after EBV infection. Notably 2-DE analysis revealed that EBV infection induced increased expression of heat shock cognate 71 kDa protein, actin cytoplasmic 1, pyridoxine-5'-phosphate oxidase, caspase 9, and t-complex protein 1 subunit alpha. In addition, EBV infection considerably suppressed those cellular proteins of zinc finger protein 2, cyclin-dependent kinase 2, macrophage-capping protein, and growth/ differentiation factor 11. Furthermore, the differential expressional levels of partial proteins (cyclin-dependent kinase 2 and caspase 9) were confirmed by Western blot analysis.Thus, this work effectively provided useful protein-related information to facilitate further investigation of the mechanisms underlying EBV infection and pathogenesis.  (+info)

Rabbit liver pyridoxamine (pyridoxine) 5'-phosphate oxidase. Purification and properties. (20/43)

Pyridoxamine (pyridoxine) 5'-phosphate oxidase (EC has been purified 2000-fold from rabbit liver. The enzyme preparation migrates as a single protein and activity band on analytical disc gels containing 4,7, or 9 percent acrylamide, and as a single protein band on sodium dodecyl sulfate acrylamide gels. The oxidase is, therefore, homogeneous by these criteria. The pure enzyme catalyzes the following reactions in the presence of FMN: (See journal for formula). These activities copurify in the ratio of 1:1:1. Apparent K-m values are 10 muM for pyridoxamine-P, 30 muM for pyridoxine-P, and 40 nM for FMN. Apparent K-m values for N-(phosphopyridoxyl)amines range from 3.1 times 10-5 M to 1.6 times 10-3 M. The dissociation constant for FMN binding, determined by quenching of protein fluorescence, is 20 nM. The pH optima for all three types of substrates are broad, with maxima near pH 9. The pH dependence of FMN binding, measured by quenching of flavin fluorescence, has the same shape as the substrate activity profile. The holoenzyme has absorption maxima red-shifted from those of FMN to 380 nm and 448 nm, and exhibits spectral changes typical of flavoproteins upon reduction with dithionite. Its oxidation-reduction potential at pH 7 in phosphate buffer is -0.131 volt. The native enzyme has a molecular weight of 54,000 and is made up of two possibly identical polypeptide chains with molecular weights of 27,000. The applicability of proposed mechanisms of flavin catalysis to this flavoprotein is discussed.  (+info)

Epilepsy due to PNPO mutations: genotype, environment and treatment affect presentation and outcome. (21/43)


Activation of a flavoprotein by proteolysis. (22/43)

Chymotryptic digestion of brain pyridoxine-5-P oxidase brings about a 4-fold enhancement of the catalytic power (Vmax/KM) using pyridoxine-5-P as substrate in the assay mixtures. The chymotrypsin-treated enzyme is less susceptible to inhibition by pyridoxal-5-P than the native enzyme. Fragments arising from limited proteolysis were separated by affinity chromatography using P-pyridoxal-Sepharose as supporting matrix. Catalytically active fractions, eluted by pyridoxine-5-P (5mM), displayed three bands when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular masses of the three protein bands are considerably lower than 28 kDa, the molecular mass of monomeric pyridoxine-5-P oxidase. Spectroscopic studies, absorption, fluorescence, and circular dichroism revealed that the microenvironment surrounding the cofactor flavin mononucleotide is not perturbed by limited proteolysis.  (+info)

Effect of tryptophan metabolites on the activities of rat liver pyridoxal kinase and pyridoxamine 5-phosphate oxidase in vitro. (23/43)

Pyridoxal kinase was purified 4760-fold from rat liver. The Km values for pyridoxine and pyridoxal were 120 and 190 microM respectively, and pyridoxine showed substrate inhibition at above 200 microM. Pyridoxamine 5-phosphate oxidase was also purified 2030-fold from rat liver, and its Km values for pyridoxine 5-phosphate and pyridoxamine 5-phosphate were 0.92 and 1.0 microM respectively. Pyridoxine 5-phosphate gave a maximum velocity that was 5.6-fold greater than with pyridoxamine 5-phosphate and showed strong substrate inhibition at above 6 microM. Among the tryptophan metabolites, picolinate, xanthurenate, quinolinate, tryptamine and 5-hydroxytryptamine inhibited pyridoxal kinase. However, pyridoxamine 5-phosphate oxidase could not be inhibited by tryptophan metabolites, and on the contrary it was activated by 3-hydroxykynurenine and 3-hydroxyanthranilate. Regarding the metabolism of vitamin B-6 in the liver, the effects of tryptophan metabolites that were accumulated in vitamin B-6-deficient rats after tryptophan injection were discussed.  (+info)

Azo dye-induced alterations in vitamin B-6 metabolism and in pyridoxal 5'-phosphate-binding proteins in rat liver. (24/43)

The effects of the hepatocarcinogen, 3'-methyl-4-dimethylamino-azobenzene, on vitamin B-6 metabolism in rat liver were studied. The following parameters were measured: pyridoxal 5'-phosphate (PLP) concentrations in plasma, brain, liver and azo dye-induced hepatomas, as well as the activities of pyridoxine (PN) kinase, pyridoxine 5'-phosphate (PNP) oxidase, PNP phosphatase and PLP-dependent ornithine decarboxylase. Hepatomas more closely resembled fetal than normal adult rat liver with respect to their ability to convert vitamer forms such as PN to coenzymatically active PLP. Microtiter plate enzyme-linked immunosorbent analyses revealed that the absence of PNP oxidase activity in a dissectable hepatoma was attributable to the absence of enzyme protein. In addition, monoclonal antibodies to vitamin B-6 were used in a Western immunoblot technique to examine the effects of azo dye ingestion on the pattern of PLP-binding proteins in cytosolic extracts of liver and hepatomas. Nitrocellulose blots of electrophoretically resolved cytosolic extracts probed for PLP-binding proteins showed increasing complexity with development; hepatomas bore a striking resemblance to fetal liver. The data indicate that hepatomas lose the properties of terminally differentiated hepatic tissue and take on the properties of fetal hepatic tissue characterized by lower concentrations of PLP, selective use of the coenzyme, and a lowered-to-absent capability to convert precursor vitamer forms to PLP. Therefore, with respect to vitamin B-6 metabolism and use, it appears likely that azo dye-induced hepatocarcinogenesis involves proliferation of a stem cell type(s) having the phenotypic characteristics of fetal hepatic tissue.  (+info)