Labeling methyl group

HSQC is based on proteins containing C-labelled methyl groups and is increasingly used to complement HSQC experiments [37]. 

A further study by Olken and collaborators112 describes inactivation of mouse iNOS by /Vc -rncl.hyI-1.-arginine. The inactivation occurs only in the presence of oxygen. Only a small amount of 3H or 14C label from the labeled methyl group of AG-methyl-L-arginine... 

The scaling factor of 40 kHz was independently determined at — 60 °C from the powder spectrum of a random dispersion of a deuteriated PM sample59. This value was furthermore confirmed in the simulations of the 2H NMR tilt series for each of the three labeled methyl groups, according to the total spectral width and line-shape arguments discussed by Ulrich and Watts58. 

FIGURE 42. 2H NMR spectra from three different bR samples containing retinals with the individually deuterium-labeled methyl groups C18, C19 and C20. Reprinted with permission from Reference 57. Copyright (1994) American Chemical Society... 

FIGURE 47. Three-dimensional structure of the cyclohexene ring of retinal in bR as determined by 2H NMR, relative to the membrane surface in the x-y plane. Analysis of the orientations of the three deuterium labeled methyl groups on the puckered ring (skew around C1-C6) indicates that the chromophore has a 6s-trans conformation around the C6-C7 bond. Reprinted with permission from Reference 60. Copyright (1997) American Chemical Society... 

With a horizontally oriented sample (a = 0°), the spectrum of the labeled bR in Figure 48(b) should display three quadrupole splittings corresponding to the three labeled methyl groups on the retinal. It is apparent, however, that the expected three pairs of resonances are not resolved because of spectral overlap of the broadened lines. A computer simulation approach was used to analyze the spectral line shapes despite the overlap, but much qualitative information about the cyclohexene ring can be gained by simple inspection of the experimental data in Figure 48. 

As previously mentioned, Kauss (40) has shown that the methyl donor for the formation of 4-methyl-D-glucuronic acid of hemicellulose B proved to be S-adenosyl-L-methionine, the same as in pectin. A particulate preparation from immature com cobs containing hemicellulose B was found capable of transferring the 14C-labeled methyl group from S-adeno-syl-L-methionine to a macromolecular acceptor present in the particles. The radioactive product was shown to be hemicellulose B labeled in the 4-methyl-D-glucuronic acid residues. It was isolated chiefly as 4-methyl-glucuronosyl-( 1 - 2)-D-xylose. 

Methylation reactions with [3H]-, [14C]- or [nC]methyliodide or [ CJmethyltriflate are widely used for the introduction of a labelled methyl group through nucleophilic substitution reactions. [3H]- and [14C]methyliodide are commercially available or can be produced as has... 

Hajduk, P. J., et al., NMR-based screening of proteins containing 13C-labeled methyl groups. JAm Chem Soc, 2000, 122, 7898-7904. 

Introduction of deuterium-labelled methyl groups into aromatic... 

In earlier work, the origin of the 3-0-methylated monosaccharides has been studied [67]. These monosaccharides do not stem from the diet, but are biosynthetically formed in the cell. It was found that only very small amounts of injected 3-G-[ H]-methyl-D-Man were incorporated into the He carbohydrate chains. However, injection of L-[methyl- C]methionine led to the incorporation of the labelled methyl group into 3MeGal of the He oligosaccharides. So far, information on the specific methyltrans-ferase(s) (Me-T) involved is not available. 

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