Search results for "methionine"

Identification and structural characterization of O-beta-ribosyl-(1"----2')-adenosine-5"-phosphate in yeast methionine initiator tRNA.

1990

We report in this paper on the complete structure determination of the modified nucleotide A*, now called Ar(p), that was previously identified in yeast methionine initiator tRNA as an isomeric form of O-ribosyl-adenosine bearing an additional phosphoryl-monoester group on its ribose2 moiety. By using the chemical procedure of periodate oxidation and subsequent beta-elimination with cyclohexylamine on mono- and dinucleotides containing Ar(p), we characterized the location of the phosphate group on the C-5" of the ribose2 moiety, and the linkage between the two riboses as a (1"----2')-glycosidic bond. Since the structural difference between phosphatase treated Ar(p) and authentic O-alpha-rib…

Amino acid contents of infant foods.

2006

The protein quality of three milk-cereal-based infant foods (paps) was evaluated by determining their amino acid contents and calculating the amino acid score. Proteins were subjected to acid hydrolysis, prior to which cysteine and methionine were oxidized with performic acid. Amino acids were determined by reverse-phase high-performance liquid chromatography with fluorescence detection with a prior derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate. Tryptophan was determined by reverse-phase high-performance liquid chromatography with ultraviolet detection after basic hydrolysis. Glutamic acid, proline and leucine were the most abundant amino acids, whereas tryptophan and …

Use of pH gradients in continuous-flow systems and multivariate regression techniques applied to the determination of methionine and cysteine in phar…

1997

Abstract The simultaneous spectrophotometric determination of methionine and cysteine in presence of cystine and other compounds in pharmaceuticals, using a multivariate calibration method, was studied. The method is based on the reaction between the analytes and the o- phthalaldehyde -N- acetyl - l - cysteine (OPA-NAC) reagent performed in a continuous-flow system (FI). The FI system allows the generation of a local pH gradient in order to produce spectral and/or kinetic changes in the UV-Vis spectra of the amino acid-OPA-NAC derivatives. This information is used to improve the prediction ability of the Partial Least-Squares (PLS) models. The performance of two FI assemblies, the selection…

Coping with Oxygen

2010

Sometime before 2.7 BYA, a new and biologically toxic substance began to appear in the environment. Biologically produced dioxygen, O2, probably first began to accumulate in small pools or layers above cyanobacterial mats. These photosynthesizers must have already developed ways to at least partially deal with dioxygen and, with greater difficulty, the reactive oxygen species (ROS) derived from it (see Chap. 1 and below). But for primitive anaerobes in the vicinity, these new substances must have been especially toxic. Nevertheless, it is clear that they evolved ways to cope with the new threats. One way was to simply avoid dioxygen altogether.

Amino Acid Contents of Infant Formulas

1999

Abstract The amino acid supply in an infant's first month of life must be sufficient in quantity and quality to fulfil the needs of this period of life. Guidelines, recommendations and minimum and maximum values have been established regarding to amino acid composition of infant formulas. The aim of this study was to determine the amino acid profile of infant formulas of different types marketed in Spain in order to assess the compliance with the recommendations (ESPGAN) and to detect possible differences in the amino acid profiles depending on the protein source. Amino acids were determined by HPLC in ion-pair reversed phase after hydrolysis and derivatization with phenylisothiocyanate. Ne…

Untersuchungen zur Aminos�ureimbalanz

1957

Potent SARS-CoV-2 mRNA Cap Methyltransferase Inhibitors by Bioisosteric Replacement of Methionine in SAM Cosubstrate

2021

Viral mRNA cap methyltransferases (MTases) are emerging targets for the development of broad-spectrum antiviral agents. In this work, we designed potential SARS-CoV-2 MTase Nsp14 and Nsp16 inhibitors by using bioisosteric substitution of the sulfonium and amino acid substructures of the cosubstrate S-adenosylmethionine (SAM), which serves as the methyl donor in the enzymatic reaction. The synthetically accessible target structures were prioritized using molecular docking. Testing of the inhibitory activity of the synthesized compounds showed nanomolar to submicromolar IC50 values for five compounds. To evaluate selectivity, enzymatic inhibition of the human glycine N-methyltransferase invol…

Determining sulfur-containing amino acids by capillary electrophoresis: A fast novel method for total homocyst(e)ine human plasma

1999

A high-performance capillary electrophoresis (HPCE) method based on laser-induced fluorescence detection is presented here. It enables the determination of sulfur-containing amino acids within 15 min. Fluorescence of sulfur-containing amino acids in plasma is linear over a range of 50-150 micromol/L for L-methionine, 5-100 micromol/L for L-homocysteine, and 50-200 micromol/L for L-cysteine. For homocysteine, we were able to detect 1 fmol injected, equivalent to a plasma concentration of 10 nmol/L. A similar sensitivity is present for cysteine, an even lower one being found for methionine. The intra- and interassay relative standard deviations are < 1%. High-performance liquid chromatography…

Acid tolerance inLeuconostoc oenos. Isolation and characterization of an acid-resistant mutant

1996

The acid tolerance ofLeuconostoc oenos was examined in cells surviving at pH 2.6, which is lower than the acid limit of growth (about pH 3.0). Acid-adapted cells survived better than non-adapted cells. Tolerance to acid stress was found to be dependent upon the adaptive pH. Acid resistance was increased by an order of magnitude for cultures adapted to a pH of about 2.9. Inhibiting protein synthesis with chloramphenicol prior to acid shock revealed that acid adaptation may involve two separate systems, one of which appears to be independent of protein synthesis. The acid-resistant mutant LoV8413, isolated during a long-term survival screen at pH 2.6, was found to be able to grow in acidic me…

Tuneable Transient Thermogels Mediated by a pH- and Redox-Regulated Supramolecular Polymerization.

2017

A multistimuli-responsive transient supramolecular polymerization of β-sheet-encoded dendritic peptide monomers in water is presented. The amphiphiles, which contain glutamic acid and methionine, undergo a glucose oxidase catalyzed, glucose-fueled transient hydrogelation in response to an interplay of pH and oxidation stimuli, promoted by the production of reactive oxygen species (ROS). Adjusting the enzyme and glucose concentration allows tuning of the assembly and the disassembly rates of the supramolecular polymers, which dictate the stiffness and transient stability of the hydrogels. The incorporation of triethylene glycol chains introduces thermoresponsive properties to the materials. …