Proteins containing reductively aminated disaccharides: Synthesis and chemical characterization

Synthetic glycoproteins can be prepared by reductive amination of protein and reducing disaccharide in the presence of sodium cyanoborohydride. The reaction proceeds readily in aqueous solutions over a broad pH range to give high degrees of substitution. The degree of substitution can be determined by amino acid analysis, as the secondary amine linkage formed by reductive amination in stable to acid-catalyzed protein hydrolysis conditions. In order to demonstrate that coupling occurs to lysine residues, synthetic α-N-1-(1-deoxyglucitol)-lysine and ?-N-1-(1-deoxyglucitol)-lysine were prepared and compared with bovine serum albumin conjugates of maltose, cellobiose, lactose, and melibiose by amino acid analysis after acid hydrolysis. These studies demonstrate that the expected secondary amine linkages are formed with the ?-amino groups of lysine.     

Identification of the active amino acid residue of the polypeptide of ATP-dependent protein breakdown

The heat-stable polypeptide of the ATP-dependent proteolytic system was previously found to form covalent conjugates with proteins and to be activated by ATP in an adenylylation mechanism. To identify the functional amino acid of the polypeptide, the activated residue was specifically labeled by the reductive cleavage of the intermediate with [3H]borohydride. Following acid hydrolysis, the reduced labeled derivative was found to be completely oxidizable by periodate with formation of [3H]formaldehyde, and was identified as ethanolamine by thin layer chromatography, electrophoresis, and amino acid analyzer chromatography. These results indicate that the activated amino acid residue of the polypeptide is COOH-terminal glycine.     

A new amino acid, 3-(2,5-SS-dicysteinyl-3,4-dihydroxyphenyl)alanine, from the tapetum lucidum of the gar (Lepisosteidae) and its enzymic synthesis.

The tapetum lucidum of the alligator gar Lepisosteus was shown by t.l.c. to contain a new phenolic amino acid, which is apparently a major constituent of the reflecting material. It was isolated in a yield of 0.5 mg/eye and its physical and chemical characteristics, especially reductive hydrolysis with hydriodic acid giving dopa (3,4-dihydroxyphenylalanine) and cysteine, suggested that it might to SS-dicysteinyldopa. Tyrosinase oxidation of L-dopa in the presence of an excess of L-cysteine yielded, in addition to known 5- and 2-S-cysteinyldopa, the same amino acid as that isolated from the eye of the gar, thus confirming the gross structure. The position of the two cysteine residues was established by the fact that tyrosinase oxidation of catechol and cyteine gave 3-S-cysteinylcatechol and 3,6-SS-dicysteinylcatechol. The natural amino acid is therefore formulated as 3-(2,5-SS-dicysteinyl-3,4-dihydroxyphenyl)alanine (2,5-SS-dicysteinyldopa), which may be formed by two consecutive additions of cysteine, first to dopaquinone and then to 5-S-cysteinyldopaquinone. The enzymic synthesis of 2,5-SS-dicysteinyldopa in vitro suggests that it may also be involved in the biosynthesis of phaeomelanin.     

New intramolecularly quenched fluorogenic peptide substrates for the study of the kinetic specificity of papain.

A series of new substrates for determining the catalytic activity of cysteine proteinases is described. The rate of hydrolysis by papain was monitored by a fluorescence continuous assay based on internal resonance energy transfer using 5-[(2-aminoethyl)amino]naphtalene-1-sulfonic acid (EDANS) and 4-(4-dimethylaminophenylazo)benzoic acid (DABCYL) as fluorescent donor and quenching acceptor, respectively, in peptides with the general structure: DABCYL-Lys-Phe-Gly-Xxx-Ala-Ala-EDANS. The substrates were used to evaluate the effect of amino acid structure in the S1' position on the kinetic parameters for papain catalyzed hydrolysis.     

Synthesis of Triamino Acid Building Blocks with Different Lipophilicities

To obtain different amino acids with varying lipophilicity and that can carry up to three positive charges we have developed a number of new triamino acid building blocks. One set of building blocks was achieved by aminoethyl extension, via reductive amination, of the side chain of ortnithine, diaminopropanoic and diaminobutanoic acid. A second set of triamino acids with the aminoethyl extension having hydrocarbon side chains was synthesized from diaminobutanoic acid. The aldehydes needed for the extension by reductive amination were synthesized from the corresponding Fmoc-L-2-amino fatty acids in two steps. Reductive amination of these compounds with Boc-L-Dab-OH gave the C4-C8 alkyl-branched triamino acids. All triamino acids were subsequently Boc-protected at the formed secondary amine to make the monomers appropriate for the N-terminus position when performing Fmoc-based solid-phase peptide synthesis.     

Antigenicities of stem bromelain. Contribution of three-dimensional structure and individual amino acid residues

The contribution of three-dimensional structure and individual amino acid residues to the antigenicities of macromolecular protein was investigated for a thiol protease stem bromelain as antigen. The extent of the participation was demonstrated by a decrease in antigenicity when the enzyme was denatured in 8 M urea before and after reductive cleavage of intrapeptide disulfide bonds or modified in particular amino acid residues. The results showed that the enzyme treated with 8 M urea without reductive cleavage of disulfide bonds preserved about 90% of antigenicity to antibodies against native stem bromelain, while the enzyme denatured after the reductive cleavage of disulfide bonds brought about almost 80% disappearance of the antigenicity. Modification of individual amino acid side chains revealed that lysine was the most immunodominant amino acid, showing 2.5% contribution per residue, and tyrosine followed with 1.2%. However, acidic amino acids such as flutamic and aspartic acids were found to be as low as 0.3%, and tryptophan was 0.2%. These data suggest that most of the antigenic determinants of stem bromelain are of the steric conformation in which lysine and/or tyrosine are most frequently involved as immunodominant amino acids.     

保护性氧化盐酸水解法分析蛋白质水解氨基酸

本文介绍了在保护剂存在下,通过过甲酸氧化,再以盐酸水解,在50分钟的分析循环时间内准确地分析17种氨基酸及三种含硫氨基酸衍生物的分析方法。     

Hydrogenation as an approach to study of reactions of oxidizing polyphenols with plant proteins

Coupling of oxidation products of o-diphenols with -NH₂ groups of plant proteins can damage nutritional availability of lysine residues. Relevant model coupling products (before or after reductive acetylation or permethylation) are unstable to acid hydrolysis. Hydrogenation over Rh/Al₂O₃, at room temperature and atmospheric pressure, gave cyclohexane derivatives stable to hydrolysis and retaining, with only partial hydrogenolysis, all groups originally attached to the aromatic nucleus. Plant bulk proteins were hydrogenated with substantial conversion of their aromatic amino acids; their S-containing amino acids were desulphurized. The technique is therefore promising for study of the fate of lysine residues in “enzymically browned” proteins.     

Synthesis of probes for the active site of leucine dehydrogenase.

A series of novel 3-substituted 2-oxobutanoic acids were prepared and incubated with leucine dehydrogenase giving in one case both a kinetic resolution at C-3 and reductive amination of the ketone. This is the first example of an amino acid dehydrogenase catalysed kinetic resolution and reductive amination.     

一个受褐飞虱取食诱导的水稻GST类似蛋白基因的克隆

BpHi006AcDNA长度为1943bp,具有一个795bp组成的完整的读码框,其表达受褐飞虱取食的诱导。BpHi006A蛋白含有谷胱苷肽S转移酶(glutathione Stransferase)的N末端结构域和C末端结构域,为谷胱苷肽S转移酶超家族的成员。BpHi006A蛋白与拟南芥四氯氢醌还原性脱卤素酶相关蛋白有61％的一致性,序列分析表明这两种蛋白质构成一类新的植物GST。     

Amino acid and peptide derivatives of the tylosin family of macrolide antibiotics modified by aldehyde function

Fourteen new functionally active amino acid and peptide derivatives of the antibiotics tylosin, desmycosin, and 5-O-mycaminosyltylonolide were synthesized in order to study the interaction of the growing polypeptide chain with the ribosomal tunnel. The conjugation of various amino acids and peptides with a macrolide aldehyde group was carried out by two methods: direct reductive amination with the isolation of the intermediate Schiff bases or through binding via oxime using the preliminarily obtained derivatives of 2-aminooxy-acetic acid.     

Rapid hydrolysis of proteins and peptides by means of microwave technology and its application to amino acid analysis

A rapid heating method of hydrolysis by the use of microwave oven has been applied to amino acid analysis of proteins and peptides. This convenient method has been compared with the conventional 6 N HCl hydrolysis at 110 degrees for 24 h. The advantages of this new method are its expedition and the accurate and comparable results as compared to the tedious conventional technique. The method provides a rapid processing of multiple samples within minutes instead of days and inexpensive access to the important data of amino acid compositions of proteins by the commonly used microwave oven. The necessary change in the design of hydrolysis vials and the safety precautions accompanying this novel use of microwave acid-digestion method are also described.     

The evaluation of the temperature effect and hydrolysis conditions for amino acid analysis

A systematic investigation of the optimal temperature and hydrolysis time for amino acid analysis has been carried out under various conditions. It is found that some simplification and increase in speed relative to the conventional protocol of employing vacuum-sealed tubes and 110 C/24-72 hour hydrolysis can be achieved without loss of accuracy and performance in amino acid analyses of proteins and peptides. The effects of hydrolysis temperature and heating time on the recoveries of various labile and hydrophobic amino acids are exemplified in the hydrolysis of oxidized ribonuclease A, lysozyme and lens crystallin. The method provides a rapid processing of multiple samples within hours instead of days with the potential for the total automation of amino acid analysis starting from the preparation of protein hydrolysates.     

13C-NMR study of acetate assimilation in Thermoproteus neutrophilus

Acetate assimilation into amino acids and the functioning of central biosynthetic pathways in the extremely thermophilic anaerobic archaebacterium Thermoproteus neutrophilus was investigated using 13C NMR as the method for determination of the labelling patterns. Acetate was assimilated via reductive carboxylation of acetyl-CoA to pyruvate and pyruvate conversion to phosphoenolpyruvate which was further carboxylated to oxaloacetate. 2-Oxoglutarate was mainly formed via citrate. However, the labelling patterns of glutamic acid and alanine were in agreement with the concurrent synthesis of about 15% 2-oxoglutarate and 5% pyruvate through the reductive citric acid cycle. A scrambling phenomenon occurring in aspartate and all amino acids derived through oxaloacetate was observed. The labelling patterns of amino acids were in agreement with their standard biosynthetic pathways, with two remarkable exceptions: isoleucine was synthesized via the citramalate pathway and lysine was synthesized via the 2-aminoadipate pathway which has previously been reported only in eukaryotic microorganisms.     

Isolation and characterization of δ-melanotropin,a new peptide from bovine pituitary glands

A new melanotropin (MSH) was isolated from bovine pituitary extract by means of gel filtration, ion exchange chromatography, high performance liquid chromatography and paper electrophoresis. Amino terminal analysis, amino acid composition and tryptic hydrolysis were performed on the purified peptide. The peptide was found to contain the amino acid sequence of γ-MSH, a theoretical segment of the proopiomelanocortin molecule. However, theoretical segment of the proopiomelanocortin molecule. However, the new peptide differs from the γ-MSH in several major ways, thus it is designated a bovine δ-MSH or δ_b-MSH.     

A new D-2-hydroxyacid dehydrogenase with dual coenzyme-specificity from Haloferax mediterranei, sequence analysis and heterologous overexpression

A gene encoding a new D-2-hydroxyacid dehydrogenase (E.C. 1.1.1.) from the halophilic Archaeon Haloferax mediterranei has been sequenced, cloned and expressed in Escherichia coli cells with the inducible expression plasmid pET3a. The nucleotide sequence analysis showed an open reading frame of 927 bp which encodes a 308 amino acid protein. Multiple amino acid sequence alignments of the D-2-hydroxyacid dehydrogenase from H. mediterranei showed high homology with D-2-hydroxyacid dehydrogenases from different organisms and other enzymes of this family. Analysis of the amino acid sequence showed catalytic residues conserved in hydroxyacid dehydrogenases with d-stereospecificity. In the reductive reaction, the enzyme showed broad substrate specificity, although alpha-ketoisoleucine was the most favourable of all alpha-ketocarboxylic acids tested. Kinetic data revealed that this new D-2-hydroxyacid dehydrogenase from H. mediterranei exhibits dual coenzyme-specificity, using both NADPH and NADH as coenzymes. To date, all D-2-hydroxyacid dehydrogenases have been found to be NADH-dependent. Here, we report the first example of a D-2-hydroxyacid dehydrogenase with dual coenzyme-specificity.     

Reactions of hydroxyamino acids during hydrochloric acid hydrolysis

Chlorosubstitution reactions occur readily during HCl hydrolysis of delta- and epsilon-hydroxynorleucines (Hnle), the products of deamination of poly-L-lysine by nitrite at low pH. During amino acid analysis, chloronorleucines elute as new peaks after delta- and epsilon-Hnle. To determine if other hydroxyamino acids undergo similar changes during hydrolysis, they were subjected individually to HCl hydrolysis conditions with and without added phenol. Amino acid analyses indicated that terminal hydroxy groups on linear side chains undergo reactions during HCl hydrolysis; the products appear as new peaks which may be chloroderivatives. In contrast, no new peaks are observed in HCl hydrolysates of delta-hydroxylysine or amino acids with beta-hydroxy groups (beta-hydroxynorvaline, serine, and threonine). Phenol did not protect linear amino acids from reactions during HCl hydrolysis but did prevent loss of the cyclic amino acids tyrosine, hydroxyproline, and 3,4-dihydroxyphenylalanine. Although the gamma-hydroxy group of homoserine would be expected to undergo reaction, HCl catalyzes its cyclization to form homoserine lactone instead.     

Comparative study on microwave and conventional methods for protein hydrolysis in food

Summary A rapid microwave hydrolysis procedure was developed for amino acid determination in food. The hydrolysis was performed with 6M HCl in sealed vessels using a microwave digestion system.Bovine Serum Albumin was chosen as a model protein to compare its theoric amino acid sequence with the experimental results obtained after hydrolysis by both the traditional oven heating and the microwave methods. Furthermore the selected microwave methods were carried out on different food matrices (cheese and durum wheat) and the obtained data were compared with the traditional method results.This comparative study shows that the rapid microwave hydrolysis is as accurate and precise as the traditional hydrolysis for determining amino acids in food.These results were presented at the Third International Congress on Amino Acids, Vienna, August 23–27th, 1993.     

A new chemical tool for characterization and partial depolymerization of red algal galactans

Complete acid hydrolysis of red algal galactans in the presence of borane - 4-methylmorpholine complex has been shown to prevent the acid degradation of 3,6-anhydrogalactose derivatives by their reduction to the corresponding 3,6-anhydro-galactitols, whereas all the other monosaccharides are liberated essentially in the non-reduced form; the reductive hydrolysis products may be determined quantitatively using gas-liquid chromatography (GLC). The method is recommended for preliminary characterization of the polysaccharide composition of red algal biomass. Partial acid hydrolysis of galactans in the presence of the same reducing agent gives rise to reduced oligosaccharides having terminal 3,6-anhydrogalactitol residues. Based on this reaction, the attribution of unknown galactans to the agar or carrageenan groups is possible by partial reductive hydrolysis of small samples of algal biomass with subsequent identification of agarobiitol or carrabiitol acetates by GLC. Sulfate groups are substantially retained under partial reductive hydrolysis conditions; the isolation by liquid chromatography and elucidation of structures of reduced sulfated oligosaccharides may be of great value for the structural analysis of complex red algal galactans.