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

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Query: EC:6.3.4.6 (urease)
7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pyrolysis gas chromatography (PGC) has been shown to be useful for differentiating enzymes. The enzymes alpha-chymotrypsin, lactate dehydrogenase, catalase, and urease were easily "fingerprinted" on a 1.8 m 0.5% Carbowax 20 M column. Also, in some cases, isoenzymes of lactate dehydrogenase could be distinguished. Based on the pyrolyses of the free aromatic amino acids, four major enzyme pyrolysis peaks were tentatively identified as organic compounds derived from tyrosine and tryptophan. The use of a nitrogen-selective detector in conjunction with the FID and measurement of peak retention times by computer on three different types of columns permitted confirmations of peak identity.
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PMID:Pyrolysis gas chromatography of enzymes. 73 Aug 12

Children with inborn errors of urea synthesis who survive neonatal hyperammonemic coma commonly exhibit cognitive deficits and neurologic abnormalities. Yet, there is evidence that ammonia is not the only neurotoxin. Hyperammonemia appears to induce a number of neurochemical alterations. In rodent models of hyperammonemia, uptake of L-tryptophan into brain is increased. It has been reported that in an experimental rat model of hepatic encephalopathy, in the ammonium acetate-injected rat, and in patients with hepatic failure and inborn errors of ammonia metabolism, quinolinate, a tryptophan metabolite, is increased. Elevations in quinolinate are of particular concern, as quinolinate could excessively activate the N-methyl-D-aspartate subclass of excitatory amino acid receptors, thereby causing selective neuronal necrosis. We sought to identify an animal model that would replicate the increases in quinolinate that have been associated with hyperammonemia in humans. Levels of quinolinate were measured in hyperammonemic urease-infused rats and ammonium acetate-injected rats. In the urease-infused rat, brain tryptophan was doubled, and serotonin and its metabolite 5-hydroxyindoleacetic acid were significantly increased. Yet, despite the increase in tryptophan and evidence for increased metabolism of tryptophan to serotonin, there were no observed increases of quinolinate in brain, cerebrospinal fluid, or plasma. In the ammonium acetate-injected rat, significant increases of 5-hydroxyindoleacetic acid in cerebral cortex were also observed, but quinolinate did not change in cerebrospinal fluid or cerebral cortex. In summary, we were unable to demonstrate an increase of quinolinate in brain or cerebrospinal fluid in these rat models of hyperammonemia.
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PMID:Quinolinate in brain and cerebrospinal fluid in rat models of congenital hyperammonemia. 127 10

The role of the anticodon and discriminator base in aminoacylation of tRNAs with tryptophan has been explored using a recently developed in vivo assay based on initiation of protein synthesis by mischarged mutants of the Escherichia coli initiator tRNA. Substitution of the methionine anticodon CAU with the tryptophan anticodon CCA caused tRNA(fMet) to be aminoacylated with both methionine and tryptophan in vivo, as determined by analysis of the amino acids inserted by the mutant tRNA at the translational start site of a reporter protein containing a tryptophan initiation codon. Conversion of the discriminator base of tRNA(CCA)fMet from A73 to G73, the base present in tRNA(Trp), eliminated the in vivo methionine acceptor activity of the tRNA and resulted in complete charging with tryptophan. Single base changes in the anticodon of tRNA(CCA)fMet containing G73 from CCA to UCA, GCA, CAA, and CCG (changes underlined) essentially abolished tryptophan insertion, showing that all three anticodon bases specify the tryptophan identity of the tRNA. The important role of G73 in tryptophan identity was confirmed using mutants of an opal suppressor derivative of tRNA(Trp). Substitution of G73 with A73, C73, or U73 resulted in a large loss of the ability of the tRNA to suppress an opal stop codon in a reporter protein. Base pair substitutions at the first three positions of the acceptor stem of the suppressor tRNA caused 2-12-fold reductions in the efficiency of suppression without loss of specificity for aminoacylation of the tRNA with tryptophan.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Conversion of a methionine initiator tRNA into a tryptophan-inserting elongator tRNA in vivo. 155 14

The middle base (U35) of the anticodon of tRNA(Gln) is a major element ensuring the accuracy of aminoacylation by Escherichia coli glutaminyl-tRNA synthetase (GlnRS). An opal suppressor of tRNA(Gln) (su+2UGA) containing C35 (anticodon UCA) was isolated by genetic selection and mutagenesis. Suppression of a UGA mutation in the E. coli fol gene followed by N-terminal sequence analysis of purified dihydrofolate reductase showed that this tRNA was an efficient suppressor that inserted predominantly tryptophan. Mutations of the 3-70 base pair (U70 and A3U70) were made. These mutants of su+2UGA are less efficient suppressors and inserted predominantly tryptophan in vivo; alanine insertion was not observed. Mutations of the discriminator nucleotide (A73, U73, C73) result in very weak opal suppressors. Aminoacylation in vitro by E. coli TrpRS of tRNA(Gln) transcripts mutated in the anticodon demonstrate that TrpRS recognizes all three nucleotides of the anticodon. The results show the interchangeability of the glutamine and tryptophan identities by base substitutions in their respective tRNAs. The amber suppressor (anticodon CUA) tRNA(Trp) was known previously to insert predominantly glutamine. We show that the opal suppressor (anticodon UCA) tRNA(Gln) inserts mainly tryptophan. Discrimination by these synthetases for tRNA includes position 35, with recognition of C35 by TrpRS and U35 by GlnRS. As the use of the UGA codon as tryptophan in mycoplasma and in yeast mitochondria is conserved, recognition of the UCA anticodon by TrpRS may also be maintained in evolution.
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PMID:Switching tRNA(Gln) identity from glutamine to tryptophan. 156 39

1. Portacaval shunting in rats results in several metabolic alterations similar to those seen in patients with hepatic encephalopathy. The characteristic changes include: (a) diminution of cerebral function; (b) raised plasma ammonia and brain glutamine levels; (c) increased neutral amino acid transport across the blood-brain barrier; (d) altered brain and plasma amino acid levels; and (e) changes in brain neurotransmitter content. The aetiology of these abnormalities remains unknown. 2. To study the degree to which ammonia could be responsible, rats were made hyperammonaemic by administering 40 units of urease/kg body weight every 12 h and killing the rats 48 h after the first injection. 3. The changes observed in the urease-treated rats were: (a) whole-brain glucose use was significantly depressed, whereas the levels of high-energy phosphates remained unchanged; (b) the permeability of the blood-brain to barrier to two large neutral amino acids, tryptophan and leucine, was increased; (c) blood-brain barrier integrity was maintained, as indicated by the unchanged permeability-to-surface-area product for acetate; (d) plasma and brain amino acid concentrations were altered; and (e) dopamine, 5-hydroxytryptamine (serotonin) and noradrenaline levels in brain were unchanged, but 5-hydroxyindoleacetic acid (5-HIAA), a metabolite of 5-hydroxytryptamine, was elevated. 4. The depressed brain glucose use, increased tryptophan permeability-to-surface-area product, elevated brain tryptophan content and rise in the level of cerebral 5-HIAA were closely correlated with the observed rise in brain glutamine content. 5. These results suggest that many of the metabolic alterations seen in rats with portacaval shunts could be due to elevated ammonia levels. Furthermore, the synthesis or accumulation of glutamine may be closely linked to cerebral dysfunction in hyperammonaemia.
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PMID:Hyperammonaemia causes many of the changes found after portacaval shunting. 170 23

A positive, genetic selection against the activity of the nitrogen regulatory (NTR) system was used to isolate insertion mutations affecting nitrogen regulation in Klebsiella aerogenes. Two classes of mutation were obtained: those affecting the NTR system itself and leading to the loss of almost all nitrogen regulation, and those affecting the nac locus and leading to a loss of nitrogen regulation of a family of nitrogen-regulated enzymes. The set of these nac-dependent enzymes included histidase, glutamate dehydrogenase, glutamate synthase, proline oxidase, and urease. The enzymes shown to be nac independent included glutamine synthetase, asparaginase, tryptophan permease, nitrate reductase, the product of the nifLA operon, and perhaps nitrite reductase. The expression of the nac gene was itself highly nitrogen regulated, and this regulation was mediated by the NTR system. The loss of nitrogen regulation was found in each of the four insertion mutants studied, showing that loss of nitrogen regulation resulted from the absence of nac function rather than from an altered form of the nac gene product. Thus we propose two classes of nitrogen-regulated operons: in class I, the NTR system directly activates expression of the operon; in class II, the NTR system activates nac expression and the product(s) of the nac locus activates expression of the operon.
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PMID:Role of the nac gene product in the nitrogen regulation of some NTR-regulated operons of Klebsiella aerogenes. 197 23

Nucleotide sequence analysis of a Ureaplasma urealyticum DNA fragment, homologous to cloned urease genes of other prokaryotes, revealed three consecutive open reading frames. The molecular weights of the three deduced polypeptides are 11.2 kD, 13.6 kD and 66.6 kD. These values are consistent with the size of the three subunits previously reported for purified native urease. A significant sequence homology was found between the three polypeptides of the ureaplasmal urease and the single polypeptide of jack bean (Canavalia ensiformis) urease. Codon usage indicates that UGA is a tryptophan codon in this mollicute. Use of polymerase chain reactions has disclosed the existence of genetic polymorphism among the urease genes of different serotypes of U. urealyticum.
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PMID:Ureaplasma urealyticum urease genes; use of a UGA tryptophan codon. 219 Nov 84

Mycoplasma capricolum uses two tryptophan codons, the "universal" nonsense codon UGA and the universal codon UGG. The bacterium contains two tryptophan tRNAs, one with anticodon UCA, (U: 2'-O-methyl U derivative), and the other with CCA (5'-C: partially 2'-O-methylated). tRNAUCA would translate codons UGA and probably UGG by wobbling. tRNACCA is much less charged by tryptophan in the cells than tRNAUCA, and the intracellular amount of tRNACCA is 5-10 times lower than that of tRNAUCA. The genes for these two tRNAs are separated by a terminator-like structure in a single operon. In vitro transcription experiments suggest that the predominance of tRNAUCA over tRNACCA results from the attenuation of transcription by this terminator-like structure.
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PMID:Evolutionary dynamics of tryptophan tRNAs in Mycoplasma capricolum. 340 3

Clues to evolution of the genetic code can be found by comparing usage of anticodons in various organisms and organelles. GC content of DNA varies, as a result of directional mutation pressure (AT/GC pressure), especially in bacteria. Low GC in Mycoplasma is accompanied by use of UGA for tryptophan and, in ciliated protozoa, by use of UAA and UAG for glutamine. These are examples of "stop codon capture," which has been preceded by duplication of tRNA genes followed by nucleotide substitutions in their sequences, including mutational changes in their anticodons. Evolutionary changes in the code may have resulted from disappearance of codons and anticodons resulting from GC pressure and from their reappearance when the direction of the pressure was reversed. In this manner, codon UGA and anticodon UCA for tryptophan could have disappeared under GC pressure and reappeared in Mycoplasma under AT pressure. Stop codon UGA may have been the third of the three stop codons to appear, originating from mutations in UAA. Changes in the code are adaptive and nondeleterious. We propose that the number of anticodons has increased and that evolution continued until three existing forms of the universal code were produced: eukaryotic, eubacterial, and the code for halobacteria and methanococci. These three codes are distinguished from each other by their anticodon pattern. The eukaryotic code contains eight INN (ANN) anticodons that have replaced GNN anticodons as a result of AT pressure. Mitochondrial and chloroplast codes have evolved from the eubacterial code through genomic economization and AT pressure, leading to losses of GNN and CNN anticodons.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Evolution of anticodons: variations in the genetic code. 345 89

The faecal carriage rates of different species of Proteeae were assessed in studies with 220 faecal isolates from 219 individuals of whom approximately one-third were well and the remainder had gastro-enteritis. As a result of the development of new media that allowed replacement of the phenylalanine deaminase test with the tryptophan deaminase test and made it possible to combine tests for indole and urease production and for hydrogen sulphide and ornithine decarboxylase formation in two single-tube tests, all strains were speciated with speed, economy and accuracy. Most (96%) isolates were either Proteus mirabilis (62%) or Morganella morgani (34%). The significance of these findings in relation to urinary tract infection is discussed. P. vulgaris was found in only one (0.45%) faecal specimen and this rarity of carriage in faeces is believed to be the main reason for its rare association with urinary tract infections. The frequent association of M. morgani, in the absence of other enteropathogenic bacteria, with severe gastroenteritis was noted with interest.
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PMID:Rare occurrence of Proteus vulgaris in faeces: a reason for its rare association with urinary tract infections. 351 39


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