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:3.1.27.4 (ribonuclease)
6,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A soluble somatostatin-binding protein was detected in the cytosol fractions of various rat, human and bovine tissues. Maximum binding occurred at pH8.0-8.5 and was Ca(2+)-dependent. The specific binding of somatostatin per 10mug of cytosol protein from 12 rat tissues ranged between 36 and 15%, and 3% for peripheral blood cells. There was also substantial binding in cytosol from human anterior pituitary and liver, and bovine anterior pituitary. The specific binding in rat and human plasma in the presence of EDTA was only 1%. Gel filtration suggested a molecular weight of approx. 80000 for the somatostatin-binding protein from several sources. Exposure of the binding protein to trypsin eliminates somatostatin-binding activity but ribonuclease and deoxyribonuclease have no effect. The binding protein is thermolabile, ethanol-precipitable, and not completely specific for somatostatin. Bound (125)I-labelled [Tyr(1)]somatostatin is not easily displaced by excess of unlabelled somatostatin. The effects of dithiothreitol and mercaptoethanol on the binding of (125)I-labelled [Tyr(1)]somatostatin to the binding protein suggests that binding involves two sequential steps, first loose binding, then disulphide linkage. Since semipurified somatostatin-binding protein causes a dose-related inhibition of the binding of (125)I-labelled [Tyr(1)]somatostatin in radioimmunoassays for somatostatin, estimates of somatostatin content of tissue extracts by radioimmunoassay in some cases may be spuriously high. It is not yet clear whether the binding protein is a true cytosol protein or an easily solubilized membrane protein.
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PMID:Properties of soluble somatostatin-binding protein. 2 54

This paper demonstrates the existence of regions in eight small globular proteins in which the side chains of sulfur-containing amino acids (cysteine and methionine) alternate in space with side chains of aromatic amino acids (histidine, phenylalanine, tryptophan and tyrosine). The proteins are: rubredoxin, high potential iron protein, cytochrome c, flavodoxin, deoxyhemoglobin, trypsin inhibitor, ribonuclease-S, and lysozyme. The sulfur-pi-bonded 'chains' involve a minimum of five and a maximum of 10 amino acids, and contain the most polarizable atoms within proteins. S-pi-chains give extra stability to the folding of proteins; they may also afford paths for the step-wise movement of electrons.
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PMID:Chains of alternating sulfur and pi-bonded atoms in eight small proteins. 20 19

Purification and partial characterization of the poliovirus RNA-linked protein (VPg) are described. VPg has been freed from the RNA by ribonuclease digestion and phenol extraction. Gel filtration chromatography of VPg-pUp (labeled with 32P) in 0.5% sodium dodecyl sulfate or 6 M guanidine HCl indicates that it has a molecular weight of about 12,000. VPg is bound to the 5' end of poliovirion RNA by a phosphodiester bond between a tyrosine residue in the VPg molecule and the 5'-terminal uridine. After acid hydrolysis of [3H]tyrosine-labeled VPg-pU, free tyrosine can be released by venom phosphodiesterase. Acid hydrolysis of VPg-p labeled with either 32P or [3H] tyrosine yields tyrosine-phosphate. There appears to be only 1 tyrosine residue per VPg molecule.
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PMID:Protein is linked to the 5' end of poliovirus RNA by a phosphodiester linkage to tyrosine. 20 34

The circular dichroism of bovine luteinizing hormone in the far ultraviolet (200-240 nm) and near ultraviolet (240-320 nm) is reported as a function of pH, reduction and denaturation. The significance of side-chain ellipticity in the native and fully randomised hormone is critically examined, using denatured and reduced ribonuclease and insulin as bases for comparison. Disulphide groups make no measurable contribution to the side-chain ellipticity. Judged by the spectra of the subunits both isolated and recombined, those treatments which promote subunit disociation without causing chain unfolding, reversibly decrease the ellipticity in the near ultra-violet with minimal effect in the far ultraviolet. Thermal perturbation difference spectroscopy of bovine luteinizing hormone and its subunits shows that, in common with the ovine and porcine hormones, there are two tyrosine residues located at the interface between the subunits and inaccessible to water. Only two or three of the five water-accessible tyrosine residues are reactive to N-acetylimidazole.
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PMID:Bovine luteinizing hormone. Circular dichroism and thermal difference spectra. 23 14

The microenvironment of histidine-48 of bovine pancreatic ribonuclease A was investigated by proton magnetic resonance spectroscopy (1H NMR) using partially deuterated enzyme in which resolution of the C(2)-H resonance of histidine-48 was simplified. The NMR titration curves at 100 and 250 MHz of histidine-48 of ribonuclease A are discontinuous both for the enzyme alone in 0.3 M chloride and for its complex with cytidine 3'-phosphate. This suggests that titration of histidine-48 occurs only as the result of a slow conformational transition. The sum of the peaks corresponding to histidine-48 in the acid-stable and base-stable forms of the enzyme is less than one proton in the transition region, which indicates that there exists at least one intermediate conformational form of the enzyme. The transition from the acid-stable form to an intermediate form has a pHmid of 5.6, and the transition from an intermediate form to the base-stable form has a pHmid of 6.9. In ribonuclease S and in ribonuclease A in the presence of 0.3 M acetate, the titration curve of histidine-48 is continuous, and the area of the peak is uniform throughout the titration. Proton NMR difference spectra at 100 and 250 MHz reveal a pH-induced conformational change with a pHmid of 5.7 that affects the chemical shift of a single tyrosine residue. This conformational transition is absent in ribonuclease S and is altered in ribonuclease A by the presence of either acetate or cytidine 3'-monophosphate. It is postulated that the same conformational transition is responsible for both the tyrosine perturbation and the disappearance of the histidine-48 peak observed in the acid-stable form of the enzyme. It is proposed that the perturbed tyrosine is tyrosine-25. The transition with pHmid 5.6 is attributed to dissociation of aspartic acid-14, and the transition with pHmid 6.9 is assigned to dissociation of histidine-48. A peak in the aromatic region that moves upfield on addition of the competitive inhibitor cytidine 3'-monophosphate is assigned to a tyrosine, and evidence is presented that this tyrosine is tyrosine-25. Inhibitor binding appears to induce a conformational change in the histidine-48/tyrosine-25 region which is remote from the active site.
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PMID:Correlation proton magnetic resonance studies at 250 MHz of bovine pancreatic ribonuclease. II. pH and inhibitor-induced conformational transitions affecting histidine-48 and one tyrosine residue of ribonuclease A. 24 Mar 91

The second derivative absorption spectra of serum albumin, insulin, ribonuclease and lysozyme were measured under various conditions to determine the state and amount of their phenylalanine residues. The second derivative spectra of these proteins were very similar to that of phenylalanine in the region between 245 and 270 nm where tryptophan and tyrosine residues caused no appreciable interference. Denaturation of proteins with urea or guanidine hydrochloride caused decrease in the intensity of the second derivative spectra, but scarcely affected the positions of peaks and troughs. The amounts of phenylalanine residues in proteins calculated from a second derivative spectra of denatured proteins coincided well with those reported in the literature. The states of the phenylalanine residues in the proteins could be deduced from the change in optical intensity on denaturation.
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PMID:Estimation of state and amount of phenylalanine residues in proteins by second derivative spectrophotometry. 39 35

Red kangaroo (Macropus rufus) ribonuclease was isolated from pancreatic tissue by affinity chromatography. The amino acid sequence was determined by automatic sequencing of overlapping large fragments and by analysis of shorter peptides obtained by digestion with a number of proteolytic enzymes. The polypeptide chain consists of 122 amino acid residues. Compared to other ribonucleases, the N-terminal residue and residue 114 are deleted. In other pancreatic ribonucleases position 114 is occupied by a cis proline residue in an external loop at the surface of the molecule. Other remarkable substitutions are the presence of a tyrosine residue at position 123 instead of a serine which forms a hydrogen bond with the pyrimidine ring of a nucleotide substrate, and a number of hydrophobichydrophilic interchanges in the sequence 51-55, which forms part of an alpha-helix in bovine ribonuclease and exhibits few substitutions in the placental mammals. Kangaroo ribonuclease contains no carbohydrate, although the enzyme possesses a recognition site for carbohydrate attachment in the sequence Asn-Val-Thr (62-64). The enzyme differs at about 35-40% of the positions from all other mammalian pancreatic ribonucleases sequenced to date, which is in agreement with the early divergence between the marsupials and the placental mammals. From fragmentary data a tentative sequence of red-necked wallaby (Macropus rufogriseus) pancreatic ribonuclease has been derived. Eight differences with the kangaroo sequence were found.
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PMID:The amino-acid sequence of kangaroo pancreatic ribonuclease. 65 39

Recovery of ribonuclease activity by complementation of peptides of barnase is reported. Activity is restored to barnase-(1-102), which lacks eight amino acids from its COOH terminus, by combination with peptides-(88-110), -(95-110), or -(99-108), and also with succinylated peptide-(88-110). The dissociation constants are about 8 X 10(-6) M for the first two combinations and little, if any, greater for the other two. Based on barnase-(1-102) concentration, up to 80% of native activity is obtained with peptide-(88-110) but only 5 to 20% with the others. The octapeptide-(103-110), equivalent to the residues missing from barnase-(1-102), does not complement barnase-(1-102), suggesting that an intact sequence about His-102 and Tyr-103 is required for activity. Barstar, the natural inhibitor of barnase, completely inhibits all activity of the complementing peptides.
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PMID:Complementation of peptides of barnase, extracellular ribonuclease of Bacillus amyloliquefaciens. 86 82

The investigation of fluorescence and light-scattering change of histone F2a, ribonuclease, tyrosine, N-acetyltirosinamide, methyl ether tyrosine by the concentration increasing of NaCl, MgCl2, Na2SO4 in the surrounding medium was carried out. In the case of used salts the changes of tertiary structure and histones aggregations depend on the anion type, which is presented in the environment. The tertiary structure of histones formed in the presence of salt is stabilized by weak (hydrophobic and hydrogenic) interactions.
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PMID:[Structure and aggregation of histones. I. Influence of the ionic composition of the medium on the structure and effectiveness of the intermolecular relationships of histone F2a (H2A+H4)]. 88

The fluorescence lifetimes and relative quantum yields of several derivatives of tyrosine are reported. The quenching of the fluorescence of these compounds by phosphate, caesium and iodide ions has been investigated; the encounter rate constants, calculated from the quenching parameters and lifetimes, show a clear dependence on the charges borne by the quenchers and fluorophores. The ratio of the Stern-Volmer constants of iodide and caesium, ions of similar size, defines an electrostatic parameter sensitive to the charge of the fluorophore which can be evaluated without knowledge of the fluorescent lifetimes. The mean of the encounter rate constants for caesium and iodide ions defines a rate constant which is largely charge-independent and is used to establish a steric parameter. The two parameters are used to investigate the tyrosine environment in bovine ribonuclease A (EC 3.1.4.23) and Erwinia carotovora L-asparaginase (EC 3.5.1.1). The quantum yield of L-asparaginase (0.12) is very high for a class A protein and may be associated with the absence of disulphide bridges. There was no evidence for more than one type of tyrosine residue from the quenching experiments with either enzyme, an observation which is attributed to efficient energy transfer amongst tyrosine residues. At pH values close to the isoelectric points of the enzymes the electrostatic parameter suggests that the environment of the quenchable tyrosines in L-asparaginase is somewhat more positive than in ribonuclease. In 1% sodium dodecyl sulphate the tyrosine environment of L-asparaginase becomes markedly negative as expected. The steric parameter indicates a lower accessibility of the tyrosine residues in L-asparaginase than in ribonuclease; an illustrative calculation is provided linking the steric parameter with the number of exposed tyrosine residues by taking into account the greater collision frequency of the larger protein molecules and the encounter distance for quenching determined from charge effects on the quenching of the model compounds. The calculation suggests that three tyrosyl residues are accessible in ribonuclease, in good agreement with other studies, but in L-asparaginase the number increases from 0.4 at pH 5.73 to 0.8 at pH 9.16 suggesting a loosening of the enzyme structure at high pH.
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PMID:An investigation of the electronic and steric environments of tyrosyl residues in ribonuclease A and Erwinia carotovora L-asparaginase through fluorescence quenching by caesium, iodide and phosphate ions. 98 70


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