Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.6.1.1 (aspartate aminotransferase)
21,665 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mitochondrial aspartate aminotransferase is inactivated by dicarbonyl reagents selectively modifying arginyl residues. Treatment with phenylglyoxal inactivates the enzyme with concomitant modification of 2.7 mol of arginyl residues/mol of subunit. If the reaction is performed in the presence of the transaminating substrate pair aspartate/oxalacetate, only 1.3 mol of arginyl residues/mol of subunit are labeled and the enzymic activity remains at 75% of the original value. One particular residue, identified by peptide analysis as Arg 292, is completely protected against modification in the presence of the substrate pair, indicating a role of its guanidinium group in substrate binding. On the basis of x-ray crystallographic studies of the complex of apoenzyme with N-(5'-phosphopyridoxyl)-aspartate (minus pyridoxal form of the enzyme), Arg 292 has been proposed as the binding site of the distal carboxylate group (Ford, G. C., Eichele, G., and Jansonius, J. N. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 2559-2563). The enzyme with blocked Arg 292 is not completely inactive, and its molecular activity toward dicarboxylic substrates is of the same order of magnitude as that of the native enzyme toward alanine, which is 10(5) times lower than that toward dicarboxylic substrates. The activity toward alanine is unchanged but the rate-enhancing effect of formate on the transamination of alanine is impaired. Formate is assumed to occupy the binding site of the distal carboxylate group (Morino, Y., Osman, A. M., and Okamoto, M. (1974) J. Biol. Chem. 249, 6684-6692). Apparently, the interaction of the distal carboxylate group of the substrate with Arg 292 underlies not only the binding specificity but also the kinetic specificity of aspartate aminotransferase for dicarboxylic substrates.
...
PMID:Chemical modification of a functional arginyl residue (Arg 292) of mitochondrial aspartate aminotransferase. Identification as the binding site for the distal carboxylate group of the substrate. 708

Native mitochondrial aspartate aminotransferase (AATase) is cleaved selectively by trypsin at the peptide bonds after Arg 26 or after Lys 31 yielding two shortened enzyme derivatives, AATase 27-410, and AATase 32-410. Recent x-ray crystallographic determination of the spatial structure of AATase has shown that the NH2-terminal segments of the two polypeptide chains of this dimeric enzyme pass in front of the active site clefts and form two separate junctions with the neighboring subunit which are not contiguous with the main subunit interface (Eichele, G., Ford, G. C., Glor, M., Jansonius, J. N., Mavrides, C., and Christen, P. (1979) J. Mol. Biol. 133, 161-180). The peptide bonds cleaved by trypsin are situated in the following stretch of the polypeptide chain which runs in exposed position on the surface of the subunit. The split-off peptide is lost during gel filtration. The molecular activity of AATase 27/32-410 (a mixture of about equal amounts of the two not readily separable derivatives) is about 3% of that of the native enzyme. In contrast, the K'm values for aspartate and 2-oxoglutarate are unchanged, indicating an unaltered geometry of the substrate binding site. A substantially diminished syncatalytic response of the reactivity of Cys 166 toward 5,5'-dithiobis-(2-nitrobenzoate) suggests that the decrease in catalytic activity is due to an interference with the syncatalytic conformational dynamics observed previously in AATase (Gehring, H., and Christen, P. (1978) J. Biol. Chem. 253, 3158-3163). Consonant with a role of the NH2-terminal segment in propagating the syncatalytic conformational rearrangements the rate of the tryptic cleavage is retarded 4-fold in the presence of the transaminating substrate pair aspartate and oxalacetate.
...
PMID:Mitochondrial aspartate aminotransferase 27/32-410. Partially active enzyme derivative produced by limited proteolytic cleavage of native enzyme. 743 Jan 25

Two peptide inhibitors of juvenile hormone biosynthesis, designated G. bimaculatus allatostatins A1 and A2, have been purified from extracts of the brain of the field cricket Gryllus bimaculatus. The primary structures of these peptides were assigned as Ala-Gln-His-Gln-Tyr-Ser-Phe-Gly-Leu-NH2 (Grb-AST A1) and Ala-Gly-Gly-Arg-Gln-Tyr-Gly-Phe-Gly-Leu-NH2 (Grb-AST A2). Each of the peptides shows C-terminal amino acid sequence similarity to cockroach allatostatins and blowfly callatostatins. The two peptides are potent inhibitors of in vitro juvenile hormone production by corpora allata from virgin females of G. bimaculatus.
...
PMID:Identification of two allatostatins from the cricket, Gryllus bimaculatus de Geer (Ensifera, Gryllidae): additional members of a family of neuropeptides inhibiting juvenile hormone biosynthesis. 748 Aug 72

Nitric oxide synthase produces NO, citrulline, water, and NADP at the expense of arginine, NADPH, and dioxygen. While citrulline has been considered to be an inert by-product of the high output inducible isoform of NO synthase (iNOS), we show here that immunostimulants induce a metabolic pathway in vascular smooth muscle cells, which enables them to regenerate arginine from citrulline. Regeneration of arginine from citrulline is accomplished by two urea cycle enzymes: arginino-succinate synthetase (AS) and argininosuccinate lyase (AL). Whereas AL is constitutive to vascular smooth muscle cells, AS mRNA and enzyme activity is markedly induced in cells by treatment with bacterial lipopolysaccharide (LPS). The induction of AS mRNA and activity by LPS follows a time course which mirrors that for iNOS but lags 1-2 h behind. As shown for iNOS, interferon-gamma does not itself induce AS but is synergistic with LPS. AS induction is suppressed by glucocorticoids, actinomycin D, and, to a lesser extent, cycloheximide. On the other hand, AS induction is unaffected by an excess of citrulline or the inhibitor of iNOS, N omega-methyl-L-arginine. Our results show the urea cycle enzymes AS and AL confer cells with the capacity to produce NO without a need for exogenous arginine. In conjunction with NOS, citric acid cycle enzymes that covert fumarate to oxaloacetate (fumarase and malate dehydrogenase) and oxaloacetate to aspartate (aspartate transaminase), AS and AL form a novel arginine-citrulline cycle that enables high output NO production by cells.
...
PMID:Argininosuccinate synthetase mRNA and activity are induced by immunostimulants in vascular smooth muscle. Role in the regeneration or arginine for nitric oxide synthesis. 751 85

The electron distribution in the coenzyme-substrate adduct of aspartate aminotransferase was changed by replacing active-site Arg386 with alanine and introducing a new arginine residue nearby. [Y225R, R386A]Aspartate aminotransferase decarboxylates L-aspartate to L-alanine (kcat = 0.04 s-1), while its transaminase activity towards dicarboxylic amino acids is decreased by three orders of magnitude (kcat = 0.19 s-1). Molecular-dynamics simulations based on the crystal structure of the mutant enzyme suggest that a new hydrogen bond to the imine N atom of the pyridoxal-5'-phosphate- aspartate adduct and an altered electrostatic potential around its beta-carboxylate group underlie the 650,000-fold increase in the ratio of beta-decarboxylase/transaminase activity.
...
PMID:Changing the reaction specificity of a pyridoxal-5'-phosphate-dependent enzyme. 755 24

Mutation of six residues of Escherichia coli aspartate aminotransferase results in substantial acquisition of the transamination properties of tyrosine amino-transferase without loss of aspartate transaminase activity. X-ray crystallographic analysis of key inhibitor complexes of the hexamutant reveals the structural basis for this substrate selectivity. It appears that tyrosine aminotransferase achieves nearly equal affinities for a wide range of amino acids by an unusual conformational switch. An active-site arginine residue either shifts its position to electrostatically interact with charged substrates or moves aside to allow access of aromatic ligands.
...
PMID:Alternating arginine-modulated substrate specificity in an engineered tyrosine aminotransferase. 766 15

Four nonapeptides that inhibit juvenile hormone synthesis have been isolated by four high performance liquid chromatographic steps from extracts of the brain of the field cricket, Gryllus bimaculatus. The primary structures of these peptides were assigned by Edman degradation and mass spectrometry as Gly-Trp-Gln-Asp-Leu-Asn-Gly-Gly-Trp-NH2 (Grb-AST B1), Gly-Trp-Arg-Asp-Leu-Asn-Gly-Gly-Trp-NH2 (Grb-AST B2), Ala-Trp-Arg-Asp-Leu-Ser-Gly-Gly-Trp-NH2 (Grb-AST B3), and Ala-Trp-Glu-Arg-Phe-His-Gly-Ser-Trp-NH2 (Grb-AST B4). Each of the peptides shows high sequence similarity to the locustamyoinhibiting peptide (Lom-MIP), but is structurally different from all the allatostatins so far identified. The synthetic allatostatins Grb-AST B1-4 are potent inhibitors (50% inhibition at 10(-8) to 7 x 10(-8) M) of juvenile hormone III biosynthesis by corpora allata from 3-day-old virgin females of G. bimaculatus using an in vitro bioassay. At 10(-7) M, Grb-AST B1 also strongly inhibits juvenile hormone III biosynthesis by corpora allata from 2-day-old adult males and 1-day-old (males and females) and 4-day-old (females) last instar larvae of G. bimaculatus. The inhibitory effect of Grb-AST B1 was also evident on corpora allata from a related species, Acheta domesticus. Inhibition of juvenile hormone synthesis by Grb-AST B1-4 is reversible.
...
PMID:A family of neuropeptides that inhibit juvenile hormone biosynthesis in the cricket, Gryllus bimaculatus. 767 41

Nitric oxide (NO) has been implicated as a mediator of hemodynamic and metabolic changes associated with endotoxemia and inflammation. In vitro studies suggest that NO inhibits hepatocyte protein synthesis but the role of NO in the regulation of hepatic protein synthesis in vivo is not known. In this study, rats were given endotoxin or saline after pretreatment with the NO synthase inhibitor NG-nitro-L-arginine or solvent, and plasma levels of nitrite (NO2), nitrate (NO3), and aspartate aminotransferase and hepatic protein synthesis rate in vivo were measured after 4 and 10 hours. The NG-nitro-L-arginine effectively blocked the increase in serum NO2/NO3 seen in endotoxemia and also inhibited the increase in hepatic protein synthesis in endotoxemic rats. The aspartate aminotransferase levels were elevated in endotoxemic rats pretreated with NG-nitro-L-arginine. Results support previous reports of a protective effect of NO on the liver in endotoxemia and suggest that NO may upregulate hepatic protein synthesis in vivo. Further study is needed to clarify the reason for the apparent difference between the effect of NO on hepatic protein synthesis in vivo and in vitro.
...
PMID:Nitric oxide may upregulate in vivo hepatic protein synthesis during endotoxemia. 767 68

Fulicin (Phe-D-Asn-Glu-Phe-Val-NH2) is an endogenous neuropeptide containing a D-amino acid from ganglia of the African giant snail Achatina fulica. We have cloned a novel cDNA (1,995 nucleotides) encoding a fulicin precursor from the snail cerebral and subesophageal ganglia. The fulicin precursor protein (357 amino acids) contains one copy of fulicin and at least nine other putative alpha-amidated neuropeptides composed of four to six amino acid residues. Seven of the nine neuropeptides were novel, and the other two had the same structures as Mytilus inhibitory peptide-related peptides previously isolated from the ganglia of Helix pomatia. All sequences of 10 peptides are flanked by Lys-Arg(Lys) at the N-terminus and by Gly-Lys-Arg(Lys) at the C-terminus. Nucleotide sequence analysis revealed that D-Asn present in fulicin is encoded by the usual L-Asn codon (AAT). Although fulicin has as yet only been isolated from the central ganglia. RNA blot analysis revealed that single transcripts of approximately 2.0 kb in size also exist in the ventricles and atria. These results suggest that fulicin and related peptides are produced in neurons and the heart by the processing of a ribosomally made precursor, although the mechanism of in-chain epimerization remains unclear.
...
PMID:A novel cDNA sequence encoding the precursor of the D-amino acid-containing neuropeptide fulicin and multiple alpha-amidated neuropeptides from Achatina fulica. 772 9

Ornithine decarboxylases from Trypanosoma brucei, mouse, and Leishmania donovani share strict specificity for three basic amino acids, ornithine, lysine, and arginine. To identify residues involved in this substrate specificity and/or in the reaction chemistry, six conserved acidic resides (Asp-88, Glu-94, Asp-233, Glu-274, Asp-361, and Asp-364) were mutated to alanine in the T. brucei enzyme. Each mutation causes a substantial loss in enzyme efficiency. Most notably, mutation of Asp-361 increases the Km for ornithine by 2000-fold, with little effect on kcat, suggesting that this residue is an important substrate binding determinant. Mutation of the only strictly conserved acidic residue, Glu-274, decreases kcat 50-fold; however, substitution of N-methylpyridoxal-5'-phosphate for pyridoxal-5'-phosphate as the cofactor in the reaction restores the kcat of E274A to wild-type levels. These data demonstrate that Glu-274 interacts with the protonated pyridine nitrogen of the cofactor to enhance the electron withdrawing capability of the ring, analogous to Asp-222 in aspartate aminotransferase (Onuffer, J. J., and Kirsch, J. F. (1994) Protein Eng. 7, 413-424). Eukaryotic ornithine decarboxylase is a homodimer with two shared active sites. Residues 88, 94, 233, and 274 are contributed to each active site from the same subunit as Lys-69, while residues 361 and 364 are part of the Cys-360 subunit.
...
PMID:Acidic residues important for substrate binding and cofactor reactivity in eukaryotic ornithine decarboxylase identified by alanine scanning mutagenesis. 774 28


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---