Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.27.1 (RNase)
 16,360 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An enzyme complex is a multifunctional catalytic unit that efficiently associates substrates with functionally related enzymes. The enzyme complex provides for the cellular regulation of enzymatic activities by physical interaction of the proteins with each other and by prior alteration of one enzyme's substrate by a related enzyme. Such regulatory abilities may go awry in neoplasia. Components of the protein biosynthetic machinery, such as aminoacyl-tRNA synthetases, have been thought to exist freely in the cytoplasm. However, high-molecular-weight enzyme complexes with aminoacyl-tRNA synthetase activities have been found in mammalian cells. We have been the first to report that the mammalian cell enzymes responsible for modification of tRNA occur in enzyme complexes (molecular weight 900000 daltons) associated with aminoacyl-tRNA synthetases and that the activities of these enzymes differ in normal and leukemic cells. Thus the enzymes responsible for the methylation of tRNA occur in enzyme complexes that provide efficient maturation of tRNA and possible regulation of protein synthesis. In FLC cells a unique enzyme complex composed of tRNA-methyltransferase and aminoacyl-tRNA synthetase activities has also been shown to contain a specific ribonuclease activity and a cysteine-tRNA sulfurtransferase activity. Sulfurtransferase activity has been characterized and optimized for its tRNA and cysteine substrates and mercaptoethanol and cation cofactors. Abnormal activity of this enzyme during neoplasia could result in improper acylation of tRNA and/or infidelity of coding by tRNA. Specific RNase is important in the sizing of percursor tRNA into mature tRNA. Results showed that this sizing was dependent upon the presence of the enzyme complex and the length of the incubation time. Many of the 20 aminoacyl-tRNA synthetases are also found in the complex. Electron microscopy has verified the subunit nature of the complex, seen previously by density gradient centrifugation and gel filtration. Three subunits, each of 300 000 daltons, comprise a complex approximately 200 A in diameter.
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PMID:Processing of tRNA is accomplished by a high-molecular-weight enzyme complex. 684 94

The aminoacylation of rat liver tRNA with selenocysteine was studied in tissue slices and in a cell-free system with [75Se]selenocysteine and [75Se]selenite as substrates. [75Se]Selenocysteyl tRNA was isolated via phenol extraction, 1 M NaCl extraction and chromatography on DEAE-cellulose. [75Se]Selenocysteyl tRNA was purified on columns of DEAE-Sephacel, benzoylated DEAE-cellulose and Sepharose 4B. In a dual-label aminoacylation with [35S]cysteine, the most highly purified 75Se-fractions were greater than 100-fold purified relative to 35S. These fractions contained less than 0.7% of the [35S]cysteine originally present in the total tRNA. When [35Se]selenocysteyl tRNA was purified from a mixture of 14C-labeled amino acids, over 97% of the [14C]aminoacyl tRNA was removed. The [75Se]selenocysteine was associated with the tRNA via an aminoacyl linkage. Criteria used for identification included alkaline hydrolysis and recovery of [75Se]selenocysteine, reaction with hydroxylamine and recovery of [75Se]selenocysteyl hydroxamic acid and release of 75Se by ribonuclease. The specificity of [75Se]selenocysteine aminoacylation was demonstrated by resistance to competition by a 125-fold molar excess of either unlabeled cysteine or a mixture of the other 19 amino acids in the cell-free selenocysteine aminoacylation system.
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PMID:Identification of a selenocysteine-specific aminoacyl transfer RNA from rat liver. 692 51

Fumarase (EC 4.2.1.2) and mitochondrial L-malate dehydrogenase (EC 1.1.1.37) were both inhibited by NaAuCl4 and KAuBr4. The inhibition for both was measured as a function of gold complex concentration and aquation time, and the NaAuCl4 inhibition was also measured in the presence of 0.15 M NaCl. Regeneration of the enzyme activity after NaAuCl4 inhibition using L-cysteine, L-methionine and NaCN was also investigated. Sodium dodecyl sulfate (SDS) acrylamide gel electrophoresis and amino acid analysis was performed on the NaAuCl4 inhibited enzymes as well as on ribonuclease A (EC 3.1.26.2), lysozyme (EC 3.2.1.17) and liver alcohol dehydrogenase (EC 1.1.1.1). It was observed that the inhibition was proportional to the gold complex concentration but decreased markedly after aquation of the complex. In the presence of NaCl the initial rate of inactivation is essentially unaffected unless the complex has been aquated and then the initial rate is increased. Gel electrophoresis on gold complex-enzyme mixtures show polymerization for ribonuclease and lysozyme and amino acid analysis indicates that no oxidation has taken place. From these results, a binding mechanism is postulated for the inhibition of the dehydrogenases by direct displacement of a halide ligand, probably by two groups on the enzyme, at least one of which may be a sulfur containing acid.
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PMID:Inhibition of two mitochondrial enzymes by gold (III) halo complexes. Evidence for a binding mechanism. 715 Dec 34

The reaction of L-3a-hydroxy-1,2,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid (Hpi) with methanethiol, ethanethiol, mercaptoethanol or 3-mercaptopropionic acid in warm aqueous acetic acid gives the corresponding 2-thioether derivatives of tryptophan in 50--80% yield (based on Hpi). Better yields may be obtained in 25% trifluoroacetic acid at room temperature. Cysteine reacts with Hpi to give the double amino acid 2-(L-3-alanylthio)-L-tryptophan (tryptathionine), which is a constituent of the highly poisonous cyclopeptides of Amanita phalloides, such as phalloidin. Reaction of a moderate excess of Hpi with cysteine-SH groups of a tripeptide (glutathione) and a protein (reduced ribonuclease) has also been effected, giving the respective S-tryptophanylated peptide or protein. In both cases, reaction occurred specifically with the -SH groups of cysteine and virtually quantitative covalent binding of tryptophan was verified. The extent of the reaction is easily quantitated by spectrophotometry or by amino acid analysis of the content of oxindolylalanine in the hydrolysate with hot 3-N p-toluenesulfonic acid of the S-tryptophanylated peptide or protein. The reaction should be useful in the field of peptide synthesis, providing a simple method for establishing a cross-link between tryptophan and cysteine, as a basic step in the chemical synthesis of toxic peptides of Amanita phalloides.
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PMID:A novel synthesis of 2-thioether derivatives of tryptophan. Covalent binding of tryptophan to cysteine sulfhydryl groups in peptides and proteins. 737 2

Rat seminal vesicle secretion is a rich source of a flavoprotein oxidase that acts upon sulfhydryl compounds. The enzyme was obtained in homogeneous form as previously described [Ostrowski, M. C., Kistler, W. S., & Williams-Ashman, H. G. (1979) Biochem. Biophy. Res. Commun. 87, 171-176] and characterized with respect to prosthetic group, size, reaction stoichiometry, and substrate specificity. On the basis of its behavior during zone sedimentation, gel filtration, and electrophoresis in the presence of sodium dodecyl sulfate, it appears to be a monomeric enzyme of about 66 000 daltons. Acid denaturation liberates 1 mol of flavin adenine dinucleotide (FAD) per mol of enzyme. The reaction catalyzed was shown to be 2RSH + O2 leads to H2O2. Superoxide formation could be demonstrated. Unlike many flavoprotein oxidases, the enzyme failed to form a bleached complex with sulfite. The enzyme accepts a variety of small sulfhydryl compounds as substrates, including glutathione, cysteine, dithiothreitol, and 2-mercaptoethanol. Michaelis-Menten kinetics were obtained with these substrates providing disulfide contamination was initially eliminated by treating thiols with borohydride. The KM for glutathione was 4.4 mM with a Vmax estimated as 660 mumol per min per mg of protein. The enzyme was capable of markedly enhancing the rate of renaturation of fully reduced ribonuclease. The physiological function of the enzyme is not yet clear, though several possibilities are discussed.
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PMID:Properties of a flavoprotein sulfhydryl oxidase from rat seminal vesicle secretion. 739 95

The aquaporins transport water through membranes of numerous tissues, but the molecular mechanisms for sensing changes in extracellular osmolality and regulating water balance in brain are unknown. We have isolated a brain aquaporin by homology cloning. Like aquaporin 1 (AQP1, also known as CHIP, channel-forming integral membrane protein of 28 kDa), the deduced polypeptide has six putative transmembrane domains but lacks cysteines at the known mercury-sensitive sites. Two initiation sites were identified encoding polypeptides of 301 and 323 amino acids; expression of each in Xenopus oocytes conferred a 20-fold increase in osmotic water permeability not blocked by 1 mM HgCl2, even after substitution of cysteine at the predicted mercury-sensitive site. Northern analysis and RNase protection demonstrated the mRNA to be abundant in mature rat brain but only weakly detectable in eye, kidney, intestine, and lung. In situ hybridization of brain localized the mRNA to ependymal cells lining the aqueduct, glial cells forming the edge of the cerebral cortex and brainstem, vasopressin-secretory neurons in supraoptic and paraventricular nuclei of hypothalamus, and Purkinje cells of cerebellum. Its distinctive expression pattern implicates this fourth mammalian member of the aquaporin water channel family (designated gene symbol, AQP4) as the osmoreceptor which regulates body water balance and mediates water flow within the central nervous system.
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PMID:Molecular characterization of an aquaporin cDNA from brain: candidate osmoreceptor and regulator of water balance. 752 31

We have previously identified a human estrogen-responsive gene, efp (estrogen-responsive finger protein), which encodes a putative transcription regulator (Inoue, S., Orimo, A., Hosoi, T., Kondo, S., Toyoshima, H., Kondo, T., Ikegami, A., Ouchi, Y., Orimo, H., and Muramatsu, M. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 11117-11121). Here, we report isolation of mouse Efp cDNA and its structure containing three cysteine-rich domains (RING finger and B1 and B2 boxes), a coiled-coil domain, and a C-terminal domain. High levels of Efp mRNA were detected in uterus, ovary, and placenta by RNase protection assay. By in situ hybridization histochemistry the transcripts of efp were also detected in uterus, mammary gland, ovary, and brain, and the co-localization of Efp and estrogen receptor mRNA was particularly demonstrated in these female organs. Moreover, the level of Efp mRNA in uterus and brain, which are known as target organs for estrogen, was up-regulated in vivo by 17 beta-estradiol. Furthermore, both the Efp and estrogen receptor mRNA were stained in the brain vesicles of 11.5-day embryos by whole mount in situ hybridization. These findings raise the possibility that efp is an estrogen-responsive gene that mediates estrogen action in various target organs.
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PMID:Molecular cloning, structure, and expression of mouse estrogen-responsive finger protein Efp. Co-localization with estrogen receptor mRNA in target organs. 759 54

Proton sharing between acidic groups has been observed in the active sites of several enzymes, including bacteriorhodopsin, aspartic proteases, and ribonuclease HI. We here report NMR observations suggestive of proton sharing between cysteine thiols in the active site of the oxidation-reduction enzyme thioredoxin. The pKas of the two cysteine thiols in the Escherichia coli protein are removed from the expected value of 8.4 by approximately 1 pH unit in either direction, upward and downward. Further, the C beta resonances of both residues show clearly the effects of both of these pKas, indicating that the titrations of the two thiol groups are intimately linked. This behavior strongly suggests that the low pKa ascribed to the deprotonation of the Cys 32 thiol most likely arises through the interaction and close approach of the thiol of Cys 35, with the thiolate anion of Cys 32 stabilized through the sharing of the remaining thiol proton, nominally attached to Cys 35. These observations provide a rationale for the mediation of active site pH control, an important aspect of the mechanism of thioredoxin and other proteins with catalytic thioredoxin domains, such as protein disulfide isomerases.
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PMID:Proton sharing between cysteine thiols in Escherichia coli thioredoxin: implications for the mechanism of protein disulfide reduction. 764 Feb 64

Expression of the alpha 1(II) procollagen gene is not confined to chondrogenic tissues during vertebrate development. Transcripts of the human gene (COL2A1) are alternatively spliced to give mRNAs which either exclude (type IIB mRNA) or include (type IIA mRNA) an exon encoding a cysteine-rich domain in the amino-propeptide. The distribution of COL2A1 mRNAs in 27- to 44-day human embryos and 8- to 24-week fetuses was studied by in situ hybridization and RNase protection analyses. Type IIA mRNAs were expressed in prechondrogenic cells and were also preferentially expressed in chondrogenic tissues at regions of chondrocyte commitment and cartilage growth. During maturation of chondrocytes, there is a switch to expression of type IIB mRNAs. In non-chondrogenic tissues of early embryos, type IIA mRNA expression was associated with active tissue remodeling, epithelial organization, and sites of tissue interaction. Type IIA mRNAs were also expressed in some non-chondrogenic tissues where expression had previously been undetected, such as the tooth bud, liver, adrenal cortex, apical ectodermal ridge, and indifferent gonad. In older fetuses type IIA mRNAs were the sole or major transcript in most non-chondrogenic tissues except the choroid plexus and tendon. In the meninges there was a unique switch from type IIB to type IIA expression. The expression pattern of COL2A1 transcripts suggests that, in addition to contributing to the structural integrity of the cartilage extracellular matrix, type II procollagen may serve a morphogenetic role in embryonic development. Our findings clearly show that the pattern of expression of type II procollagen mRNAs is largely conserved between man and mouse. However, some differences exist, and these should be taken into consideration when animal models are used to study human diseases associated with COL2A1.
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PMID:Tissue-specific and differential expression of alternatively spliced alpha 1(II) collagen mRNAs in early human embryos. 765 82

The polypeptide inhibitor of the ribonuclease barnase, barstar, has two cysteine residues in positions 40 and 82. These have been proposed to form a disulfide bridge leading to an increase in stability without changing the inhibitory activity of the protein. Barstar and a mutant (E80A) were oxidized in vitro and the biochemical and physico-chemical properties of the oxidized monomers were analysed. The oxidized proteins show no inhibition of barnase using a plate assay and are significantly destabilized. CD spectra indicate a loss of secondary structure. The amino acid substitution E80 --> A stabilizes the oxidized barstar to about the same extent as it does the reduced protein, indicating, however, that the helical region which it is in is intact.
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PMID:Characterization of in vitro oxidized barstar. 765 92


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