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)

Pyridine borane has been reported as a superior reagent over a wide pH range, 5-9, for the reductive methylation of amino groups of proteins with formaldehyde [J. C. Cabacungan , A. I. Ahmed , and R. E. Feeney (1982) Anal. Biochem. 124, 272-278]. It has also been reported to reduce tryptophan to dihydrotryptophan and to inactivate lysozyme in trifluoroacetic acid [M. Kurata , Y. Kikugawa , T. Kuwae , I. Koyama , and T. Takagi (1980) Chem. Pharm . Bull 28, 2274-2275]. In the present study the specificity of pyridine borane for the two different modifications under different reaction conditions has been demonstrated, and extended to the application to the synthesis of protein containing reductively attached carbohydrates. In the acid reduction, pyridine borane selectively reduced all six tryptophans in lysozyme to dihydrotryptophan while all other amino acids remained intact. On similar treatment no cleavage of the carbohydrate moiety from chicken ovomucoid, and no losses of activity of ovomucoid or ribonuclease, two proteins devoid of tryptophan, were observed. Nearly complete methylation of the lysines of lysozyme, chicken ovomucoid, and ribonuclease was achieved with formaldehyde at pH 7.0 after 2 h at room temperature, with the retention of full activity of the protein without any destruction of tryptophan. The same chemistry was applied to covalently attach glucose and lactose to bovine serum albumin. Parameters, including pH, temperature, and methanol, that affect the reactions were investigated. Incremental additions of pyridine borane during the course of the reactions increased the rate of modification. The covalent attachment of sugar to the epsilon-amino group of lysine was demonstrated by the synthesis of N-alpha- acetylglucitollysine and comparison with acid hydrolysates of the bovine serum albumin-sugar derivatives.
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PMID:Pyridine borane as a reducing agent for proteins. 643 Jan 22

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

Ribonuclease inhibitor (RI) was purified about 1300-fold from human cerebrum (including a small portion of midbrain) by a combination of ammonium sulfate precipitation, ribonuclease A-Sepharose chromatography, and high-performance anion-exchange chromatography. The purified RI appeared to be homogeneous as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Using the same method, a homogeneous RI was also obtained from human hindbrain (brainstem and cerebellum). The cerebral RI appeared to be virtually identical with the hindbrain RI on the basis of the following properties: (a) Molecular mass was estimated to be 50 kDa on SDS-PAGE under reducing conditions. (b) Composition analysis revealed that the RI was rich in leucine and cysteine residues and included no amino sugars. (c) The N-terminus was blocked and probably modified by N-acetylation. After treatment with trifluoroacetic acid, it became susceptible to Edman degradation and was sequenced as Ser-Leu-Asp-Ile-Gln-Ser-Leu-Asp-Ile-Gln-(Cys)-Glu-Glu-. (d) The RI, which showed sulfhydryl-dependent inhibitory activity on both secretory-type and nonsecretory-type ribonucleases, bound tightly to ribonuclease to form a 1:1 complex on a molar basis. (e) The RI cross-reacted strongly with anti-human placental RI antibody. These findings also indicate that human brain RI is quite similar to human placental RI. In contrast to the abundance of RI in human brain tissue (about 0.08% (w/w) of total protein), RI was undetectable in human cerebrospinal fluid, suggesting that brain RI may not be a secreted protein.
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PMID:Purification and characterization of human brain ribonuclease inhibitor. 803 55

A method, which utilizes microwave-assisted partial acid hydrolysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), to elucidate oligosaccharide composition of intact glycoproteins is presented here. Glycoproteins, such as ribonuclease B, avidin, alpha1-acid glycoprotein, and fetuin, are used as model systems to demonstrate this technique. Partial cleavage of oligosaccharides from whole intact glycoproteins with trifluoroacetic acid was observed after a short exposure to microwaves. Due to the high-resolution mass spectra obtained by MALDI-TOFMS from glycoproteins with molecular weights less than 20 kDa, the compositions of oligosaccharides are readily derived for ribonuclease B and avidin. The data agree with the proposed oligosaccharide structures of ribonuclease B (five glycoforms) and avidin (eight glycoforms). Larger glycoproteins such as alpha1-acid glycoprotein (many glycoforms) and fetuin (many glycoforms) exhibited only broad peaks with no glycoform resolution. Nevertheless, this method can be used successfully for analysis of glycoproteins with molecular weights greater than 20 kDa to determine the presence or absence of glycosylation.
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PMID:Characterization of oligosaccharide moieties of intact glycoproteins by microwave-assisted partial acid hydrolysis and mass spectrometry. 1612 37