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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A gamma-aminobutyric acid transferase (4-aminobutyrate:2-oxoglutarate aminotransferase; EC 2.6.1.19) preparation from Nippostrongylus brasiliensis was found to contain only one peak of enzyme activity with a highly basic pI of 10.5 when analysed by isoelectric focusing and chromatofocusing. This material was used in kinetic studies to demonstrate that the parasite enzyme reaction mechanism conforms to the usual binary, non-sequential ('Bi Bi Ping Pong') type found with aminotransferases. The Km for 4-aminobutyrate was 0.33 mM, the Km for 2-oxoglutarate was 0.57 mM and Ki for glutamate was 0.35 mM. In holoenzyme reconstitution experiments with the cofactor, pyridoxal 5-phosphate, the KD was 1.54 microM. The values are comparable to those reported for other tissues. Only 2-oxoglutarate could function as the keto acid substrate whereas several amino acids besides 4-aminobutyrate (beta-alanine, alpha-L-alanine, L-aspartate and L-arginine) could apparently act as substrate although the possible presence of other amino acid:2-oxoglutarate aminotransferases was not excluded. In preliminary studies on the usefulness of conventional substrate analogues as parasite gamma-aminobutyric acid transferase inhibitors only canaline was effective.
Mol Biochem Parasitol 1984 Jun
PMID:Kinetics of 4-aminobutyrate:2-oxoglutarate aminotransferase from Nippostrongylus brasiliensis. 648 5

The enzyme, aspartate aminotransferase, is a dimer consisting of two identical subunits which contain overlapping subunit regions ( Eichele , G., Ford, G.C., Glor , M., Jansonius , J.N., Mavrides , C., and Christen , P. (1979) J. Mol. Biol. 133, 161-180), suggesting the possibility of subunit interactions. The structurally similar cytosolic isozyme exhibits noncooperative binding of pyridoxal 5'-phosphate ( Boettcher , M., and Martinez -Carrion, M. (1975) Biochemistry 14, 4528-4531; Relimpio , A., Iriarte , A., Chlebowski , J.F., and Martinez -Carrion, M. (1981) J. Biol. Chem. 256, 4478-4488) in which the apoenzyme/holoenzyme hybrid dimer shows a distinctive thermal stability. Using a nonequilibrium isoelectric focusing technique, it can be shown that mitochondrial aspartate aminotransferase also binds cofactor in a noncooperative random fashion. However, differential scanning calorimetry (DSC) thermograms show different characteristics from the cytosolic form. These differences are interpreted in terms of unique subunit interactions in this isozyme. Heating to the various DSC transition temperatures shows that the anomalous DSC thermograms in partially coenzyme-saturated apoenzyme preparations are due to a selective dissociation of apoenzyme subunits into monomers which are irreversibly denatured. The remaining holoenzyme monomers reassociate and form stable holoenzyme dimers. The net result is retention of the initial concentration of holoenzyme subunits present in any given mixture. Random occupancy of active sites and similar electrophoretic and DSC patterns upon heating of partially saturated apoenzyme preparations is observed whether the coenzyme, pyridoxal phosphate or pyridoxamine phosphate alone, or borohydride-reduced Schiff's bases of coenzyme-substrate analogue derivatives are used as active site directed ligands. The latter resemble covalent enzyme-substrate intermediates.
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PMID:Coenzyme active site occupancy as an indicator of independence of the subunits of mitochondrial aspartate aminotransferase. 672 80

Circular dichroism (CD) spectra of glycogen phosphorylase a and b from rabbit liver have been measured in the presence of various ligands in the near- and far-ultraviolet regions. Positive circular dichroism was detected in the absorption band of protein-bound pyridoxal phosphate (333 nm). The mean residue ellipticity of this dichroic band (35 deg cm2dmol-1) is of the same order for muscle and liver phosphorylase a and b and does not change upon binding of glucose-1-phosphate and AMP. Only glucose induces small changes in the ellipticity in this region. The CD spectra of muscle and liver phosphorylase a and b in the 250-300 nm region have at least five positive dichroic bands namely at 259, 264, 273, 281 and 288 nm and have strong resemblances for all these forms of the enzyme in spite of the fundamental differences in their properties. The binding of AMP and glucose to phosphorylase from both sources induces distinct perturbations in CD spectra; the changes are much larger for muscle and liver phosphorylase a than for phosphorylase b which indicates that conformational perturbations induced by binding of activator and inhibitor to the inactive form of phosphorylase are probably more local than for the active form. The CD spectra in far-ultraviolet region are similar for all forms of phosphorylase. The percent of alpha-helices calculated according to Chen is about 50; this value coincides very well with the value 51% received for muscle phosphorylase a by X-ray crystallographic analysis at 2.5 A resolution.
Mol Biol (Mosk)
PMID:[Comparative study of the circular dichroism of rabbit liver and muscle glycogen phosphorylases a and b]. 677 57

Interactions of pyridoxal phosphate and its analogs (at pH 6.0) with dimeric glutamate apodecarboxylase (E. coli) were examined by spectrophotometric and CD-titration and by gel electrophoresis. It was shown that 5 equivalents of pyridoxal-phosphate fully restore the catalytic activity and optical properties of the enzyme, whereas 3 equivalents of the coenzyme suffice for reconstitution of the hexameric structure. Similar amounts of the 2 nor PLP adn 5'-methtyl PLP restore the hexameric macromolecule. 15 equivalents of pyridoxine phosphate or 54 -- of pyridoxamine phosphate are required for complete saturation of the apoenzymes binding sites and concomitant reconstitution of the hexameric structure. 5'-deoxy-5'-carboxymethyl pyridoxal, 5'-deoxy-5'-phosphonomethyl pyridoxal and cis-5'-deoxy-5'-phosphonomethylen pyridoxal were merely bound to the dimeric apoenzyme, but failed to restore the enzyme's quaternary structure. Pyridoxal, trans-5'-deoxy-5'-posphonomethylen pyridoxal and pyridoxine analogs substituted in position 5' with carboxyl or phosphonyl group did not interact with the apodecarboxylase.
Mol Biol (Mosk)
PMID:[Effects of pyridoxal-phosphate and its 4'- and 5'-substituted analogs on macromolecular structure of Escherichia coli glutamate decarboxylase]. 704 67

Phosphorylases (EC 2.4.1.1) from potato and rabbit muscle are similar in many of their structural and kinetic properties, despite differences in regulation of their enzyme activity. Rabbit muscle phosphorylase is subject to both allosteric and covalent controls, while potato phosphorylase is an active species without any regulatory mechanism. Both phosphorylases are composed of subunits of approximately 100 000 molecular weight, and contain a firmly bound pyridoxal 5'-phosphate. Their actions follow a rapid equilibrium random Bi Bi mechanism. From the sequence comparison between the two phosphorylases, high homologies of widely distributed regions have been found, suggesting that they may have evolved from the same ancestral protein. By contrast, the sequences of the N-terminal region are remarkably different from each other. Since this region of the muscle enzyme forms the phosphorylatable and AMP-binding sites as well as the subunit-subunit contact region, these results provide the structural basis for the difference in the regulatory properties between potato and rabbit muscle phosphorylases. Judged from CD spectra, the surface structures of the potato enzyme might be significantly different from that of the muscle enzyme. Indeed, the subunit-subunit interaction in the potato enzyme is tighter than that in the muscle enzyme, and the susceptibility of the two enzymes toward modification reagents and proteolytic enzymes are different. Despite these differences, the structural and functional features of the cofactor, pyridoxal phosphate, site are surprisingly well conserved in these phosphorylases. X-ray crystallographic studies on rabbit muscle phosphorylase have shown that glucose-1-phosphate and orthophosphate bind to a common region close to the 5'-phosphate of the cofactor. The muscle enzyme has a glycogen storage site for binding of the enzyme to saccharide substrate, which is located away from the cofactor site. We have obtained, in our reconstitution studies, evidence for binding of saccharide directly to the cofactor site of potato phosphorylase. This difference in the topography of the functional sites explains the previously known different specificities for saccharide substrates in the two phosphorylases. Based on a combination of these and other studies, it is now clear that the 5'-phosphate group of pyridoxal phosphate plays a direct role in the catalysis of this enzyme. Information now available on the reaction mechanism of phosphorylase is briefly described.
Mol Cell Biochem 1982 Feb 19
PMID:Potato and rabbit muscle phosphorylases: comparative studies on the structure, function and regulation of regulatory and nonregulatory enzymes. 706 10

After in vitro labelling of androgen receptors in prostate tissue from castrated rats, about 70% of the labelled androgens in nuclei could be extracted with buffer solutions with 0.4 M KCl, or 10 mM pyridoxal phosphate, or 0.4 mM Cibacron blue, or heparin (0.2 mg/ml). In the nuclear extracts, 60-80% of the steroid was recovered as steroid-receptor complex. Sedimentation values of the receptors, on sucrose gradients containing 0.4 M KCl, were 3-4 S for the KCl extract and 4-5 S for pyridoxal phosphate and heparin extracts. The Cibacron blue extract contained an aggregated form of the receptor (5-7 S). The presence of the protease inhibitor di-isopropylfluorophosphate during isolation caused a small increase in S value of the receptors. However, the differences in sedimentation values between KCl, pyridoxal phosphate and heparin extracts remained. The receptors in the KCl extracts could be precipitated with protamine sulphate only after addition of 10 mM pyridoxal phosphate to the extracts. On the basis of these results it is concluded that the androgen receptors in rat prostate can be effectively extracted from nuclei by certain reagents which have in common a strongly negatively charged group and a less polar or hydrophobic region. These reagents form complexes with nuclear receptors and influence the sedimentation values and precipitability with protamine sulphate of these receptors.
Mol Cell Endocrinol 1981 Sep
PMID:Extraction of nuclear androgen receptors from rat prostate with different reagents. 728 83

Histidine, arginine, tyrosine, lysine and cysteine residues of protein S1 were modified with diethyl pyrocarbonate & rose bengal, 2,3-butanedione (diacetyl), tetranitromethane, pyridoxal 5-phosphate, and N-ethyl-maleimide, respectively. Modification of the residues and the number of modified residues were determined by either fluorescence or UV spectroscopy. The effect of chemical modification on the function of protein S1 was studied with respect to nucleic acid (poly U and M13 ssDNA) binding and ribosome binding properties of the protein. We tested S1 binding to these two types of polynucleotides because of their reported (Draper et al. (1977) PNAS 74, 4786-4790) binding to two different sites on S1. The results indicate that histidine and lysine residues of S1 play an important role in the binding of S1 to both types of nucleic acids and that histidine and to some extent tyrosine residues are involved in the binding of S1 to ribosomes. The Data indicate the need for a re-evaluation of the two nucleic acid binding-site model.
Biochem Mol Biol Int 1994 Nov
PMID:Amino acid functional groups involved in the binding of Escherichia coli ribosomal protein S1 to ribosomes and nucleic acids. 753 16

cDNAs encoding P2x purinoceptors from human bladder smooth muscle and from rat PC-12 cells were expressed in oocytes and human embryonic kidney 293 cells. Agonist potencies of 2-methylthio-ATP = 2-chloro-ATP = ATP > = 2'- and 3'-O-(4-benzoylbenzoyl)-ATP > or = adenosine-5'-O-(3-thio)-triphosphate > or = P1,P5-di(adenosine-5') pentaphosphate >> ADP prevailed for both P2x purinoceptors. There were two main differences in agonist sensitivity between the two receptors. First, ATP was 10 times more potent at the receptor from bladder (EC50, 0.8 microM) than at the receptor from PC-12 cells (EC50, 8.2 microM). Second, alpha,beta-methylene-ATP and L- and D-beta,gamma-methylene-ATP were agonists in cells expressing the bladder smooth muscle receptor (EC50, 1-3 microM) but were ineffective in cells expressing the PC-12 receptor. The P2 purinoceptor antagonists suramin, pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid, and pyridoxal-5-phosphate acted similarly at both receptor forms, producing noncompetitive inhibition, with IC50 values of 1-5 microM for suramin and pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid and 10-20 microM for pyridoxal-5-phosphate. 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid distinguished receptor subtypes, producing potent inhibition of the bladder smooth muscle P2x-mediated response, with an IC50 value of 3 microM; it inhibited the PC-12 form by < 40% at 100 or 300 microM. This study thus defines the pharmacological properties of homo-oligomeric forms of these two types of cloned P2x receptor channels.
Mol Pharmacol 1995 Aug
PMID:Pharmacological characterization of heterologously expressed ATP-gated cation channels (P2x purinoceptors). 754 32

The interaction of glutamate decarboxylase with the aspartate analogues 3-arsonoalanine and 3-phosphonoalanine, with the glutamate analogues 2-amino-4-arsonobutyric acid and 2-amino-4-phosphonobutyric acid, and with 4-(methylthio)-L-glutamic acid, both as a mixture of diastereoisomers and as the (2S,4R)-form, was studied. All these analogues were poor substrates for the enzyme and only weak inhibitors. Their decarboxylation was accompanied by transamination of the enzyme-bound pyridoxal phosphate (PLP) to pyridoxamine phosphate (PMP), thus inactivating the decarboxylase. With arsonoalanine only part of the PLP was converted into PMP.
Biochem Mol Biol Int 1995 May
PMID:The interaction of glutamate decarboxylase from Escherichia coli with substrate analogues modified at C-3 and C-4. 766 23

We have identified and sequenced an hdc gene in the Vibrio anguillarum plasmid pJM1 which encodes a histidine decarboxylase enzyme and is an essential component for the biosynthesis of anguibactin. The open reading frame corresponds to a protein of 386 amino acids with a calculated molecular mass of 44,259.69 Da. The amino acid sequence has extensive homology with the pyridoxal-P-dependent histidine decarboxylases of Morganella morganii, Klebsiella planticola, and Enterobacter aerogenes. Tn3-HoHo1 transposition mutagenesis of the hdc gene present in a recombinant clone carrying the entire pJM1 iron uptake region produced two derivatives, one with the lacZ gene in the same orientation as the direction of hdc transcription and the other with the lacZ gene in the opposite orientation. A. V. anguillarum strain harbouring one of the mutated derivatives was unable to grow under iron-limiting conditions and did not produce anguibactin. Therefore, the hdc gene must play a role in the biosynthetic pathway of this siderophore and consequently in conferring the high virulence phenotype to this bacterium. The role of histidine decarboxylase in biosynthesis of anguibactin was confirmed by the fact that growth under iron starvation was restored by addition of histamine to the medium. The presence of anguibactin was also demonstrated in supernatants from cultures of the hdc mutant strains grown under iron starvation with the addition of histamine, further confirming that histamine is a precursor in the biosynthesis of the siderophore.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Microbiol 1995 Jan
PMID:A histidine decarboxylase gene encoded by the Vibrio anguillarum plasmid pJM1 is essential for virulence: histamine is a precursor in the biosynthesis of anguibactin. 775 99


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