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Biomedical subjects

E Bayer

Publications and source records attributed to E Bayer.

At least 73 records · Page 4Linked to original sources
PubMed1982

Syntheses of 4-[N-(tert-butoxycarbonyl)aminoacyloxymethyl]-3-nitrobenzoic acids for use in the liquid-phase peptide synthesis.

The syntheses of 4-(Boc-aminoacyloxymethyl)-3-nitrobenzoic acids are described. These compounds are suitable reagents for coupling to polyethylene glycol or its derivatives by the dicyclohexylcarbodiimide method to obtain 4-(Boc-aminoacyloxymethyl)-3-nitrobenzoyl-polyethylene glycol support. This is demonstrated by the reaction of the 4-carboxy-2-nitrobenzyl ester of Boc-alanine with glycylpolyethylene glycol in excellent yield. This synthetic route produces a much better coupling yield and an easier purification procedure in comparison with the original method in which Boc-amino acid cesium salts are allowed to react with 4-(bromomethyl)-3-nitrobenzoyl-polyethylene glycol.

Amino Acids↗
PubMed1981

Synthesis of histone model sequences for immobilization on a cross-linked polyacrylate matrix.

The synthesis of three peptide sequences which are useful as histone models, [Lys]5, [Lys]5-Pro and the sequence 17-27 of the lysine-rich histone from rabbit thymus Pro-Ala-Lys-Lys-Lys-Lys-Ala-Ala-Lys-Lys-Pro is described. Three different methods for the synthesis are applied. [Lys] 5 is synthesized from the amino end beginning with N alpha-acryloyl-N epsilon-Cbo-lysine by successive coupling of Cbo-lysine to yield the pentalysine monomer CH2=CH-CO-[Lys(Cbo)]5 which can be used directly for radical copolymerization. [Lys]5-Pro is synthesized according to the conventional peptide synthesis using the carbobenzoxy group for N alpha-protection and the tert,-butyl group for side chain protection. The carboxyl function is protected as tert.-butyl ester. The undecapeptide is synthesized in a similar manner. Instead of purifying the intermediate peptides by extraction, chromatography is used exclusively. The isolation of the unprotected peptides Lys-Pro, [Lys]3-Pro, [Lys]4-Pro, [Lys]5-Pro and Pro-Ala-[Lys]4-[Ala]2-[Lys]2-Pro and their characterization using amino acid analysis, electrophoreses and field desorption mass spectrometry is also reported.

Acrylic Resins↗
PubMed1981

Evidence from inhibitor studies for conformational changes of citrate synthase.

1. Substrate analogue CoA derivatives were applied as inhibitors of citrate synthase. Substitution of the acyl-CoA oxygen next to sulfur by hydrogen was without marked influence on the affinity. 2. Carboxymethyl-CoA, a structural analogue of enolic acetyl-CoA, was characterized as a transition state analogue by an affinity 100-fold higher than that of acetyl-CoA. Ks of the binary inhibitor-enzyme complex was high (230 microM) but that of the ternary inhibitor-oxaloacetate-enzyme complex was 0.07 microM. Both enzyme subunits bound the inhibitor independently, also in the presence of oxaloacetate. 3. (3R,S)-3,4-Dicarboxy-3-hydroxybutyl-CoA, an analogue of citryl-CoA, inhibited the overall reaction noncompetitively against acetyl-CoA and against oxaloacetate; it was a competitive inhibitor against the hydrolysis and cleavage reactions of (3S)-citryl-CoA. Kinetic data suggest that this inhibitor represents an intermediate analogue. 4. The results given above indicate conformational changes of the synthase during the catalytic cycle. In the proposed mechanism the free enzyme represents a hydrolase which in the presence of oxaloacetate, by a well-known conformational change, is converted into a ligase. If both substrates are present, the ligase is reconverted into the hydrolase upon formation of the intermediate, (3S)-citryl-CoA.

Acetyl Coenzyme A↗
PubMed1980

A new gas chromatographic method for determination of amino acid levels in human serum.

Amino acid levels of biological fluids are usually determined by the classical ion exchange procedure. Although the gas chromatographic method offers the advantage of higher sensitivity and speed of analysis, apparent difficulties in achieving accuracy and precision similar to the ion exchange procedure prevented its acceptance as a routine method. The main problems associated with gas chromatographic amino acid analysis were overcome by application of a novel approach called enantiomer-labelling: the optical antipode to each L-amino acid is added to the sample prior to the clean-up and serves as an internal standard having identical chemical properties. The enantiomers of all amino acids are separated by gas chromatography on capillaries coated with a thermally stable, chiral stationary phase. The shortcomings previously inherent in the gas chromatographic method are thus eliminated. Accuracy and precision of the new procedure are equal or better than of the classical ion exchange method.

Adult↗
PubMed1979

Synthesis of the C-terminal decapeptide of bovine insulin B-chain.

The liquid-phase synthesis of a decapeptide corresponding to the last 10 amino acid residues of bovine insulin B-chain is described. Modified monofunctional polyethylene glycol containing benzyl bromide functional group was used as the soluble polymeric support. Cleavage of the fully-protected peptide from the polymer was achieved with 1N NaOH in dioxane. The protected peptide was purified by chromatography on Sephadex LH-20. The protecting groups of a sample were removed with anhydrous HF, and the unprotected crude decapeptide was purified by ion-exchange chromatography on carboxymethyl-cellulose. Both peptides were tested for the racemization of individual amino acids by the gas chromatographic method. The results showed that no residue had been significantly racemized.

Animals↗
PubMed1978

Enantiomer labelling, a method for the quantitative analysis of amino acids.

Enantiomer labelling a method for the quntitative analysis of optically active natural compounds by gas chromatography, involves the use of the unnatural enantiomer as an internal standard. With Chirasil-Val, a chiral stationary phase that is thermally stable up to up to 240 degrees, the enantiomers of amino acids and a variety of other compounds can be separated and quantitated. Incomplete recovery from the sample, incomplete derivatization, hydrolysis and thermal decomposition of the derivative and shifting response factors can be compensated for by adding the unnatural enantiomer. The accuracy of amino acid analysis by enantiomer labelling is equal or superior to that of hitherto known methods. The procedure affords a complete analysis of peptides with respect to both amino acid composition and the optical purity of each amino acid.

Amino Acids↗
PubMed1978

Gas chromatographic--mass spectrometric analysis of optically active metabolites and drugs on a novel chiral stationary phase.

Chirasil-Val, a novel chiral polysiloxane-type stationary phase is capable of separating the enantiomers of optically active drugs and metabolites of several compound classes; alpha-amino acides, alpha-amino alcohols, glycols, aromatic and aliphatic alpha-hydroxy carboxylic acids and amines. Due to their high thermal stability, columns coated with Chirasil-Val may be coupled to a mass spectrometer. Potential applications of the new stationary phase include analysis of the optical purity of enantiomeric drugs, determination of the configuration of metabolites, and quantitation of optically active drugs and metabolites using the unnatural enantiometer as internal standard. Direct separation of enantimoers on Chirasil-Val is especially useful if only minute amounts of the optically active compounds are availalbe for analysis.

Chromatography, Gas↗
PubMed1978

[Cytological studies of sputum and bronchial secretions (author's transl)].

Cytological diagnosis was achieved in 89 of 206 (43.2%) malignant lung tumours verified histologically. The quality of cytological material, number of examinations, tumour size and differentiation, as well as careful handling of the material and experience of the cytologist, all influenced the rate of false-negative results. Cytological examination of sputum and bronchial secretions gave a higher rate of detecting malignant lung tumours than histological examination of material obtained by bronchoscopy.

Biopsy↗
PubMed1978

On the significance of the prosthetic group composition of citrate lyase.

1. Klebsiella aerogenes contains two different acyl carrier proteins, one specific for citrate lyase, the other for fatty acid synthetase. 2. The acyl carrier protein of fatty acid synthetase from K. aerogenes was isolated and compared with the corresponding protein from Escherichia coli and with the acyl carrier protein of citrate lyase from K. aerogenes. 3. As judged from prosthetic group compositions as well as amino acid and fingerprint analyses, the acyl carrier proteins of the two fatty acid synthetases are nearly identical but different from that of citrate lyase from K. aerogenes. 4. Therefore, the different prosthetic groups alone cannot be responsible for the different specificities of the acyl carrier proteins of fatty acid synthetase and citrate lyase in K. aerogenes. 5. The prosthetic group of citrate lyase, phosphoribosyl dephospho-CoA, apparently represents no incidental, phosphopantetheine-replacing aberration. The requirement of citrate lyase for the CoA-like prosthetic group may arise from the substrate requirement of both subunit enzymes of the enzyme complex.

Amino Acids↗
PubMed1977

Rapid gas chromatographic separation of amino acid enantiomers with a novel chiral stationary phase.

The use of novel polysiloxanes as stationary phase carrying chiral groups enables the separation of most amino acid enantiomers in a much shorter time than ever reported previously. Phases of this type exhibit very low volatility and high thermal stability and may be used in routine analysis with open tubular columns ant temperatures of at least 175 degrees C. Most protein amino acids are separated in a temperature program between 90 and 175 degrees C, thus obviating the need for multiple injections. Resolution factors are somewhat lower than those of other diamide phases containing the L-valine t-butyl-amide group, but are sufficient for resolution of almost all protein amino acid enantiomers.

Amino Acids↗
PubMed1977

The solid phase synthesis of porcine secretin with full biological activity.

The solid phase synthesis of procine secretin is described. The C-terminal residue was attached to a polymeric amino support and all the Boc-amino acids, including Boc-glutamine, were coupled by a modified carbodiimide method. A preliminary test synthesis showed that the couplings of several amino acids of the N-terminal section were unsatisfactory. This problem was overcome in the main synthesis by executing all the major reactions twice. Cleavage of the peptide fromthe resin as well as the removal of all the side chain protecting groups was achieved with liquid HF. The product was purified by ion-exchange chromatography on SP-Sephadex to obtain a highly purified heptacosapeptide amide with full biological activity.

Amino Acid Sequence↗
PubMed1976

[Cytological classification of bronchial carcinoma (author's transl)].

Reliability of cytological classification of tumours from material obtained from sputum or bronchial secretion was tested on 116 histologically confirmed cases of bronchial carcinoma. Squamous-cell carcinoma and small-cell undifferentiated carcinoma were most often correctly classified, results being less good with large-cell undifferentiated carcinoma, adenocarcinoma taking an intermediary position.

Adenocarcinoma↗