Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nucleotide sequence of cDNA for bovine aromatic L-amino acid decarboxylase (AADC) was analyzed. The deduced amino acid sequence of bovine AADC shows 57% identity to drosophila AADC and 37% to plant Catharanthus roseus AADC. The 7-amino acid sequence of the pyridoxal phosphate binding site is completely conserved among drosophila, pig and bovine AADC. AADC primary structure also shows high homology to that of feline glutamic acid decarboxylase.
Brain Res Mol Brain Res 1990 Jun
PMID:Deduced amino acid sequence of bovine aromatic L-amino acid decarboxylase: homology to other decarboxylases. 216 4

We report that pdxA, which is required for de novo biosynthesis of pyridoxine (vitamin B6) and pyridoxal phosphate, belongs to an unusual, multifunctional operon. The pdxA gene was cloned in the same 3.5-kilobase BamHI-EcoRI restriction fragment that contains ksgA, which encodes the 16S rRNA modification enzyme m6(2)A methyltransferase, and apaH, which encodes diadenosine tetraphosphatase (ApppA hydrolase). Previously, Blanchin-Roland et al. showed that ksgA and apaH form a complex operon (Mol. Gen. Genet. 205:515-522, 1986). The pdxA gene was located on recombinant plasmids by subcloning, complementation, and insertion mutagenesis, and chromosomal insertions at five positions upstream from ksgA inactivated pdxA function. DNA sequence analysis and minicell translation experiments demonstrated that pdxA encoded a 35.1-kilodalton polypeptide and that the stop codon of pdxA overlapped the start codon of ksgA by 2 nucleotides. The translational start codon of pdxA was tentatively assigned based on polypeptide size and on the presence of a unique sequence that was also found near the translational start of PdxB. This conserved sequence may play a role in translational control of certain pyridoxine biosynthetic genes. RNase T2 mapping of chromosomal transcripts confirmed that pdxA and ksgA were members of the same complex operon, yet about half of ksgA transcripts arose in vivo under some culture conditions from an internal promoter mapped near the end of pdxA. Transcript analysis further suggested that pdxA is not the first gene in the operon. These structural features support the idea that pyridoxine-biosynthetic genes are members of complex operons, perhaps to interweave coenzyme biosynthesis genetically with other metabolic processes. The results are also considered in terms of ksgA expression.
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PMID:Overlap between pdxA and ksgA in the complex pdxA-ksgA-apaG-apaH operon of Escherichia coli K-12. 267 Aug 94

L-Arginine stimulates the respiration of Leishmania donovani to rates comparable to those observed with D-glucose. gamma-Guanidinobutyramide, CO2, urea and succinate have been identified as products of L-arginine catabolism by the cell-free extract. The reactions involved in CO2 and urea formation require aerobic conditions. An enzymatic reaction that converts radiolabelled L-arginine to gamma-guanidinobutyramide occurs in cell-free extracts. The enzyme catalyzes a reaction in which O2 consumption and CO2 production are equimolar. The O2 uptake and CO2 production are stimulated by Mg2+, Mn2+, FMN, pyridoxal phosphate, and inhibited by hydroxylamine and NaBH4. L-Arginine decarboxyoxidase is suggested as the trivial name for this enzyme. The enzyme has maximum activity at pH 6.7, and its Km for L-arginine is 3.8 mM. L-Arginine decarboxyoxidase initiates the catabolism of L-arginine (pH less than or equal to 7) in this species, and is followed by the other enzymes of gamma-guanidinobutyramide pathway. Assay procedures have been devised to assay the multiple enzymes of this pathway.
Mol Biochem Parasitol 1987 Apr
PMID:The gamma-guanidinobutyramide pathway of L-arginine catabolism in Leishmania donovani promastigotes. 360 Jun 96

Renal cysteine conjugate beta-lyase (beta-lyase) catalyzes the bioactivation of nephrotoxic cysteine S-conjugates. beta-Lyase activity is present in both renal cytosolic and mitochondrial fractions, and, although the cytosolic beta-lyase is identical to glutamine transaminase K, the mitochondrial beta-lyase has not been characterized. Because beta-lyase is a pyridoxal phosphate (PLP)-dependent enzyme, pyridoxamine phosphate (PMP) formation may occur during the metabolism of cysteine S-conjugates. In this study, the effects of alpha-ketoacids, which may convert the PMP form of the enzyme to the pyridoxal phosphate form, on the metabolism and cytotoxicity of cysteine S-conjugates were examined; the PMP enzyme is catalytically inactive in beta-elimination reactions, but is catalytically active in transamination reactions. Both alpha-keto-gamma-methiolbutyrate (KMB) and alpha-ketobutyrate enhanced the metabolism of S-(2-benzothiazolyl)-L-cysteine (BTC) to 2-mercaptobenzothiazole by rat renal cytosol or mitochondria. KMB and phenylpyruvate potentiated both the cytotoxicity of S-(1,2-dichlorovinyl)-L-cysteine (DCVC) in isolated rat renal proximal tubular cells and the inhibition of mitochondrial respiration produced by DCVC. These results are consistent with the formation of PMP during the renal cytosolic or mitochondrial metabolism of cysteine S-conjugates. Mitochondrial beta-lyase was previously localized in the outer membrane. To examine whether beta-lyase activity is present in mitoplasts, but in the PMP form, the effects of KMB on the metabolism of BTC to 2-mercaptobenzothiazole and on the DCVC-induced inhibition of state 3 respiration in mitoplasts were studied. The majority of the mitochondrial beta-lyase activity was present in the outer membrane, and the specific activity of the outer membrane beta-lyase was greater than that of the mitoplast beta-lyase. KMB produced equivalent stimulation of beta-lyase activity in intact mitochondria, in mitochondrial outer membranes, and in mitoplasts and potentiated DCVC-induced inhibition of respiration in intact mitochondria, but not in mitoplasts. These results provide additional evidence for the central role of beta-lyase in the bioactivation of nephrotoxic cysteine S-conjugates.
Mol Pharmacol 1987 Feb
PMID:Alpha-ketoacids stimulate rat renal cysteine conjugate beta-lyase activity and potentiate the cytotoxicity of S-(1,2-dichlorovinyl)-L-cysteine. 380 95

The spatial structure of cytosolic chicken aspartate aminotransferase (AAT) has been determined by X-ray crystallographic analysis at 2.8 A resolution. AAT consists of two chemically identical subunits. Each subunit can be subdivided into the large pyridoxal phosphate (PLP) binding domain and the small domain. The two active sites of AAT are situated in deep clefts at the subunit interface. The binding of PLP and 2-oxoglutarate is described. Conformations of the following enzyme forms have been compared by difference Fourier syntheses: the nonliganded PLP-form in phosphate and acetate buffers; the non-liganded pyridoxamine phosphate (PMP) form; complexes of the PLP-form with glutarate and 2-oxoglutarate. Lattice-induced dynamic asymmetry of the dimeric AAT molecules was revealed. In one subunit the small domain is mobile and shifted either toward the active site ("closed" conformation) or in the opposite direction ("open" conformation). The closed conformation is induced by the binding of dicarboxylate anions. In the second subunit the small domain is immobile and shifted toward the active site in all enzyme forms or complexes studied. In this subunit, there occurs a rotation of the PLP ring by approximately 20 degrees toward the substrate site. The rotation is observed when crystals are soaked in 0.6 saturated (NH4)2SO4 solution buffered with 0.3 M potassium phosphate, pH 7.5; it was explained by formation of an external aldimine between PLP and NH3. This aldimine is not formed in the presence of dicarboxylates or acetate. It was inferred that dicarboxylate or acetate anions stabilize the internal PLP-lysine aldimine and prevent its reaction with ammonia. Conversion of AAT from the PLP- to PMP-form is accompanied by rotation of the coenzyme ring by approximately 20 degrees; the rotation occurs in both subunits.
Mol Biol (Mosk)
PMID:[Cytosol aspartate aminotransferase from the chicken heart: three-dimensional structure at 2.8 angstroms resolution and the characteristic conformation of various enzyme forms]. 398 8

Cytosolic chicken heart aspartate aminotransferase (EC 2.6.1.1) was incorporated in polyacrylamide gel and partially oriented by compressing the gel block in two mutually perpendicular directions. The linear dichroism (LD) was recorded in a dichrograph equipped with a quarter-wavelength device which transforms circularly polarized light into linearly polarized. Spectra were resolved with lognormal distribution curves. A marked difference has been found between reduced linear dichroism values (LD/A) in the absorption bands of the protonated (430 nm) and nonprotonated (360 nm) forms of the internal pyridoxal phosphate--lysine aldimine. This finding indicates that protonation of the internal aldimine bond induces a change in direction of the transition dipole moment within the coenzyme ring or reorientation of the ring. Formation of the external aldimine with 2-methylaspartate is accompanied by a decrease of the reduced LD value in the 430 nm band. On the other hand, binding of the dicarboxylate anions, which imitates formation of the noncovalent adsorption Michaelis complex, results in a marked increase of the reduced LD value in the 430 nm band. These data suggest that the coenzyme ring tilts in opposite directions upon noncovalent substrate binding and upon subsequent formation of the external aldimine.
Mol Biol (Mosk)
PMID:[Linear dichroism of chicken cytosol aspartate aminotransferase oriented in polyacrylamide gel]. 407 36

The formation of GABA from L-glutamate was investigated in homogenates of rat brain, liver, and kidney, using highly purified [14C]-L-glutamic acid as substrate and a thin-layer chromatographic separation of products. In agreement with other workers, liberation of [14C]-CO2 was found to be stoichiometric with GABA formation in brain homogenates, but not in liver or kidney extracts. Subcellular fractionation and dialysis experiments suggested that most of the GABA synthesis in these peripheral tissues, unlike brain, does not occur via a direct decarboxylation of glutamate and requires one or more cofactors other than pyridoxal phosphate. NAD stimulated GABA formation in dialyzed extracts, and inhibition of GABA-transaminase, both in vitro and in vivo, caused marked inhibition of GABA formation from glutamate in peripheral extracts. Although a very low GAD activity in liver and kidney cannot be excluded, these experiments suggest a major pathway from glutamate to GABA in these homogenates which includes (1) conversion of glutamate to alpha-ketoglutarate by glutamate dehydrogenase or transaminases, (2) conversion of alpha-ketoglutarate to succinic semialdehyde, and (3) formation of GABA from succinic semialdehyde and glutamate by GABA-transaminase.
Mol Cell Biochem 1981 Sep 25
PMID:Glutamate as a precursor of GABA in rat brain and peripheral tissues. 611 23

The substrate-promoted inactivation of glutamate decarboxylase from hog brain was studied. Inactivation was a slow process that was dependent on the concentration of glutamate. Glutamate-dependent inactivation was not first order but was best described as the sum of two exponential decay processes. At 10 mM glutamate, the half-lives at 30 degrees C were about 6 min for the fast component and 70 min for the slow component. Glutamate-dependent inactivation appeared to be due to the formation of apoenzyme since the rate and extent of inactivation were greatly reduced by the presence of pyridoxal 5'-phosphate (the cofactor, pyridoxal-P). Also, inactivated enzyme could be reactivated by adding pyridoxal-P (Meeley and Martin, 1983). Micromolar concentrations of ATP enhanced glutamate-promoted inactivation in the absence of pyridoxal-P. ATP also enhanced inactivation in the presence of 10 microM pyridoxal-P, but somewhat higher concentrations were required for an equal effect. ATP had little or no direct effect on the enzyme in the absence of glutamate. In the absence of pyridoxal-P, Pi reduced the enhancement of inactivation by 10 microM but not by 750 microM ATP. Glutamate-promoted inactivation, its enhancement by ATP, and the opposition to inactivation by pyridoxal-P and Pi appear to be important in the regulation of glutamate decarboxylase.
Cell Mol Neurobiol 1983 Mar
PMID:Inactivation of brain glutamate decarboxylase and the effects of adenosine 5'-triphosphate and inorganic phosphate. 613 27

Aspartate aminotransferase is a pyridoxal phosphate-dependent enzyme that catalyses the transamination reaction: L-aspartate + 2-oxoglutarate----oxaloacetate + L-glutamate. The enzyme shuttles between its pyridoxal and pyridoxamine forms in a double-displacement process. This paper proposes a mechanism of action that delineates the dynamic role of the protein moiety of this enzyme. It is based on crystallographically determined spatial structures (at 2.8 A resolution) of the mitochondrial isoenzyme in its unliganded forms and in complexes with substrate analogues, as well as on model building studies. The enzyme is composed of two identical subunits, which consist of two domains. The coenzyme is bound to the larger domain and is situated in a pocket near the subunit interface. The proximal and distal carboxylate group of dicarboxylic substrates are bound to Arg386 and Arg292 , respectively, the latter residue belonging to the adjacent subunit. These interactions largely determine the substrate specificity of the enzyme. They not only position the substrate efficient catalysis but also bring about a bulk movement of the small domain that closes the active site crevice and moves Arg386 about 3 A closer to the coenzyme. The replacement of the epsilon-amino group of Lys258 by the alpha-amino group of the substrate in the aldimine bond to pyridoxal phosphate is accompanied by a tilting of the coenzyme by approximately 30 degrees. The released epsilon-amino group of Lys258 serves as a proton acceptor/donor in the 1,3- prototropic shift producing the ketimine intermediate. At this stage, or after hydrolysis of the ketimine bond, the coenzyme rotates back to an orientation between that in the "external" aldimine intermediate and that in the pyridoxal form. Throughout this process, the protonated pyridine nitrogen atom maintains a hydrogen bond to the beta-carboxylate group of Asp222 . Upon formation of the pyridoxamine form, the small domain moves back to its original position. The proposed mechanism is compatible with the known kinetic and stereochemical features of enzymic transamination.
J Mol Biol 1984 Apr 15
PMID:Mechanism of action of aspartate aminotransferase proposed on the basis of its spatial structure. 614 29

Cytochrome c is modified by covalent binding of pyridoxal phosphate (PLP) to lysine residues. One di-substituted [(PLP)2--C] and two mono-substituted derivatives [(PLP)--c and (PLP)''--c] were obtained and precisely purified. The peak at 695 nm and CD-spectra in 190--600 nm region show that all derivatives have native conformation. The differential UV-spectra of the derivatives against native protein show that in (PLP)2--c there is a contact dipole-dipole interaction between PLP chromophores. It is calculated that the N-atoms of the two PLP-substituted lysines must be at a distance less than or equal to 12 A. Analysing our and literature data, one may suppose that Lys-13 and Lys-87 are the most probable candidates for modification with PLP. (PLP)---c and (PLP)''--c behave differently during ion-exchange chromatography and when added to cytochrom c-depleted mitochondria. (PLP)''--c restores electron transfer at higher concentrations than (PLP)'--c. Both they restore fully succinate and ascorbate oxidation but at considerably higher concentrations than the native protein, i. e. modification of any one of the reactive towards PLP lysines descreases but does not exclude the interaction with its reductase and oxidase. The effective equilibrium constants of binding of modified derivatives to cytochrome c-depleted mitochondria are lower than the constant for native protein. Together with decrease in binding activity, Hill coefficients increase. From our results it may be supposed that probably the binding sites of cytochrome c for its reductase and oxidase partially overlap.
Mol Biol (Mosk)
PMID:[Pyridoxalphosphate-modified derivatives of cytochrome c. Mono- and disubstituted derivatives: characteristics and effect on electron transport in cytochrome c-depleted mitochondria]. 624 46


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