PHOTOCHEMICAL ADDITION OF AMINO ACIDS AND PEPTIDES TO DNA

Abstract— The quantum yields for photochemical addition of twenty of the amino acids commonly occurring in proteins to denatured calf thymus DNA have been determined in deoxygenated phosphate buffer at λ 254 nM and pH 7 using a fluorescamine assay technique. Fifteen were found to be reactive, with cysteine, lysine, phenylalanine, tryptophan and tyrosine being the most reactive. Alanine, aspartic acid, glutamic acid, serine and threonine were unreactive. Analogous quantum yields for a series of eighteen peptides of the form glycyl X (X being one of the commonly occurring amino acids) were also determined, along with the corresponding quantum yields for L-alanyl-L-alanine, L-alanyl-L-tryptophan, L-seryl-L-seryl-L-serine, L-threonyl-L-threonyl-L-threonine, and L-cystine- bis -glycine. All of the peptides were found to be reactive. The modified amino acids N^ε-methyllysine, N^ε, N^ε, N^ε-trimethyllysine and N^ε-acetyllysine, all occurring in minor amounts in the histone group of chromosomal proteins, were also found to be reactive as was N^α-acetyllysine. The quantum yields for photoaddition of a selected group of amino acids and peptides to denatured DNA and native DNA are compared. In some cases higher quantum yields for photoaddition to denatured DNA are observed while in other cases the reverse is true. The effect of oxygen on the quantum yields for photoaddition of selected peptides to DNA was examined. While for most systems studied the amount of reaction in aerated systems was less than in deoxygenated systems, in the case of glycyl-L-phenylalanine the reverse was true.     

REACTIVITY OF SINGLET OXYGEN TOWARD AMINO ACIDS AND PEPTIDES

Quenching of singlet oxygen (¹O₂) in D₂O-ethanol by the amino acids tryptophan, tyrosine, histidine, methionine, cysteine and their derivatives was measured by exciting the sensitizers rose bengal or meso-tetra (N-methyl-4-pyridyl)porphyrin tetratosylate in the presence of oxygen and the above quenchers in solution. In our polar solvent, containing 75% D₂O on a molar basis it was found that (1) substitution of the aromatic ring in indole, phenol and imidazole by the electron-donating methyl group increases the total (i.e. nonreactive and reactive) quenching rate constant by a factor of five to eight. Free or blocked amino and carboxyl groups removed by two methylene groups from the ring counteract the above increase in the rate constant. The reactive quenching of singlet oxygen, which leads to oxidative destruction of the aromatic ring, correlates with the above substitution effects. It has been proposed that the quenching process takes place by formation of an exciplex between ¹O₂ and the quencher. Thus our results indicate that the better an electron donor the amino acid residue is the more pronounced is the charge transfer contribution in the exciplex formed with ¹O₂ and the more likely it is to lead to charge separation and hence to a chemical reaction. (2) Oligopeptides in solution or peptide bonds linked to the amino acid residue have only a minor effect on singlet oxygen. It can therefore be expected that the polypeptide chains per se in the protein network will not interact significantly with the single oxygen molecules present. The quenching of the latter should, to a first approximation, depend only on the presence of the above reactive amino acid residues and to their accessibility to ¹O₂ as well as on the effective dielectric constant within the protein structure.     

PHOTOCHEMICAL ADDITION OF AMINO ACIDS AND PEPTIDES TO POLYURIDYLIC ACID

Abstract— The quantum yields for photochemical addition of glycine and the L-amino acids commonly occurring in proteins (excluding proline) to polyuridylic acid have been determined in deoxygenated phosphate buffer at pH 7, using a fluorescamine assay technique. All twenty amino acids were found to be reactive, with cysteine, tryptophan, phenylalanine, tyrosine, arginine, lysine and methionine being the most reactive. The analogous quantum yields for a series of eighteen dipeptides of the form glycyl X (X being one of the commonly occurring amino acids, including proline), of L-alanyl-L-tryptophan, of the tripeptides L-seryl-L-seryl-L-serine and L-threonyl-L-threonyl-L-threonine, of the tetrapeptide L-cystine- bis -glycine, and of the lysine derivative N_α-acetyllysine were also measured. All were found to be reactive toward photoaddition to poly U.     

SYNTHESIS OF NEW ESTRONE DERIVATIVES OF AMINO ACIDS AND PEPTIDES

A series of estrone derivatives of amino acids and peptides haze beensynthesized by different coupling reagents and the binding affinity of deblocked derivativesto the estrogen receptor of rats uteri have been measured by a comptetive radiometric bind-ing assay.     

FLASH PHOTOLYSIS STUDY OF ALIPHATIC AMINO ACIDS AND PEPTIDES IN AQUEOUS SOLUTION*

Abstract— The intermediates produced in the photolysis of oxygen-free aqueous solutions of a number of aliphatic amino acids and peptides were observed spectrophotometrically using the fast-reaction technique of flash photolysis. Included among the compounds examined are the N-acetyl derivatives of glycine, alanine, sarcosine, glutamic acid and glycylglycine; the esters and amides of these N-acetyl compounds; diketopiperazines; the amino acids glycine, alanine and β-alanine; and finally the oligopeptides di-, tri- and tetraglycine. The direct optical excitation of these compounds was found to lead primarily to a photo-induced decarboxylation reaction:
The transient spectra of the radicals produced have been identified. The quantum yields of these processes were found to be directly proportional to the p K _a of the carboxyl groups of the corresponding ground-state molecules, and hence to the concentration of the non-ionized carboxylic acids. The φ's of these processes for the ionized acids were close to zero. The dependence of φ upon pH is correlated to the absorption spectra of these compounds. The quantum yields of the corresponding esters were lower but independent of pH. No intermediates were observed from excitation of the amine derivatives. Other photolytic reactions are suggested. The photo-decarboxylation of alanine and diglycine were found to be monophotonic, while that of N-acetyl alanine, N-acetyl diglycine, and tetraglycine were found to be biphotonic. A triplet excited state precursor is indicated for the latter group of compounds. These and other results are discussed.     

PREPARATION OF METHYL ESTER DERIVATIVES OF AMINO ACIDS BEARING HYDROLYSABLE N-PROTECTION

ABSTRACT

A convenient method for the esterification of amino acids bearing labile N-substituents is described. Three compounds, 2(a–c), have been synthesised with retention of an N-trifluoroacetamide or an enamine group.     

N-PHOSPHORYL AMINO ACIDS AND PEPTIDES: PART I. THE CRYSTAL AND MOLECULAR STRUCTURE OF N-(O,O-DIISOPROPYL PHOSPHORYL)-TRANS-4-HYDROXY-D,L-PROLINE

Abstract

The crystal and molecular structure of N-(O,O-diisopropyl phosphoryl)-trans-4-hydroxy-D,L-proline has been determined by X-ray diffraction analysis and is compared with proline or hydroxyproline residue in a peptide chain described in the literature. The compound crystallized in orthorhombic system with space group P2₁2₁2₁, a=6.934(2), b=8.694(3), c=26.727(7) Å, V=1611.3(8) ų, Z=4, Dx=1.22 g/cm³. The structure was solved by direct method and refined by anisotropic least squares to a discrepancy index R=0.072. In the compound, the nitrogen atom is trigonal and its remaining 2p orbital is conjugated with the P?Oπ system; the conformation of the phosphorimidate function is favoured by the trans orientation of the P=O bond with respect to the N-C4 bond. In the pyrrolidine ring moeity, the C2-C1-N-C4 atoms are nearly copolnar and the C3 atom is out of the plane by about 0.47 Å.     

OPTICALLY ACTIVE BIS(BIQUANIDE)COBALT(III) COMPLEXES CONTAINING AMINO ACIDS

Abstract

Biguanide-amino acid complexes of the type Co(am)(Hbg)³⁺ ₂, where am is the anion of glycine, sarcosine, L-alanine, L-valine, L-isoleucine, or L-proline, have been prepared and resolved. The absorption, circular dichroism (CD) and proton magnetic resonance spectra (for the alanine and valine complexes) are reported. For some salts of some of the complexes of optically active amino acids, one pure optical isomer could be obtained by slow crystallization from from the reaction solution. One optical isomer of the complexes containing optically active amino acids is present in the reaction mixture to a slightly greater extent than the other. The effects of hydroxide ion and heating on equilibration was studied. Assignments of absolute configurations were made from the CD spectra.     

PREPARATION OF N-ACYL DERIVATIVES OF AMINO ACIDS FROM ACYL CHLORIDES AND AMINO ACIDS IN THE PRESENCE OF CATIONIC SURFACTANTS. A VARIATION OF THE SCHOTTEN-BAUMANN METHOD OF BENZOYLATION OF AMINO ACIDS

A very efficient method for the preparation of N-acylamino acids from the corresponding acyl chloride and amino acid is described. Amino acids, potassium carbonate, acyl chloride, and a catalytic amount of cationic surfactants were mixed in tetrahydrofuran and refluxed without ever obtaining a clear reaction mixture. After hot filtration, the product was isolated from the hot tetrahydrofuran solution in very high or almost quantitative yields.     

SYNTHESIS OF CHIRAL THIOCARBAMOYLPHOSPHINES DERIVED FROM AMINO ACIDS1

Abstract

The methylester hydrochlorides of the (S)-amino acids L-alanine (la), L-phenylalanine (1b), L-valine (1c) and L-lysine (1d) were converted to the corresponding isothiocyanates 2a-d by thiophosgenation. 2a-d react with secondary phosphines and phosphine oxides to give the thiocarbamoylphosphines 3a-d and P-oxides 4a, b.     

COMPLEX EQUILIBRIA INVOLVING TRIPHENYLTIN(IV) SOME SELECTED AMINO ACIDS AMD NUCLEOTIDES

Abstract

Complex formation equilibria for triphenyltin(IV) with selected aminoacids and nucleotides having a variety of model functional groups were studied. Stoichiometries and stability constants for the complexes formed were determined by a potentiometric technique, in 75% dioxane- water solution amino acids and nucleotides are bound to PhSn(IV) as monodentates. The effect of the pK_a of the amino acid on the stability constant of its complex species was elucidated. Concentration distributions of the various complex species were evaluated as a function of pH.     

碱性氨基酸离子交换平衡特性的研究

研究了碱性氨基酸与001×7阳离子交换树脂的离子交换平衡特性。测定了001×7树脂对碱性氨基酸两种价态离子的选择性吸附系数,并考察了pH和碱性氨基酸的浓度对平衡吸附量的影响,确定了离子交换的最佳pH 和碱性氨基酸的浓度。     

PHOTOSENSITIZATION OF AMINO ACIDS BY DI-CYAN-HEMIN: KINETIC AND EPR STUDIES

Abstract— The low spin hemin derivative di-cyan-hemin can sensitize the photooxidation of amino acids. The efficiency of this dye as a photosensitizer is generally lower than that of other porphyrins such as hematoporphyrin in aqueous solution, but it is significantly enhanced by addition of ethanol. On the basis of the identified photooxidation end-products of some amino acids, photooxidation kinetic data and EPR measurements, it appears that methionine is quantitatively converted to methionine sulfoxide by a pure Type II (singlet oxygen) mechanism, whereas in the case of cysteine and tryptophan a mixed Type ILType II mechanism is probably operative.     

ABSORPTION AND FLUORESCENCE STUDY OF TYROSINE-DERIVED CROSSLINKING AMINO ACIDS FROM COLLAGEN

Isotrityrosine, an isomer of trityrosine with an ether linkage, is a new crosslinking amino acid recently found in cuticle collagen of Ascaris lumbricoides . The absorption and fluorescence spectra of this new amino acid were examined and compared with other tyrosine-derived crosslinking amino acids. Isotrityrosine showed UV absorption maximum at 283 nm in acidic and neutral solutions and at 303 nm in strongly basic solution. The wavelengths are almost the same with those at dityrosine and trityrosine. The values of p K _a, for chromophore phenols are 7.5 and 11.0. This means that two proton dissociations occur progressively one by one. Boric acid did not have any influence on isotrityrosine, though the effect on dityrosine and trityrosine was substantial. These facts mentioned above may suggest structural inequality of two phenols in an ether-linked isomer. The wavelength of emission maximum was 450 nm, which was the longest wavelength among relative compounds examined. The fluorescence quantum yield was as small as 0.027, and the value was about one-tenth of those of dityrosine and trityrosine. Isotrityrosine was also found in cuticle collagen of other worms which belong to the phylum nematoda.