Methyl labelling

Table III gives the titration parameters for the C resonances of the N-terminal mono[ C]methyl labels of a variety of peptides and glycopep-tides related to the N-terminus of glycophorins and A. The titration...

Methylphenol is carboxylated to 2-methyl-4-hydroxybenzoate by a methanogenic-enrich-ment culture before degradation to acetate (Figure 8.44a) (Roberts et al. 1990) C-labeled bicarbonate prodnced carboxyl-labeled acetate, while C-methyl-labeled 3-methylphenol yielded methyl-labeled acetate. However, 2-methylbenzoate formed by dehydroxylation of 2-methyl-4-hydroxybenzoate was not further metabolized (Figure 8.44b). A similar reaction occnrs with a sulfate-reducing mixed culture (Ramanand and Suflita 1991). 

Radioactive 11C-methyl labeling for study of methanol co-reaction with methyl iodide on Fe -Beta zeolite... 

For both ethanol and 1-propanol, co-feeding of methylene- and methyl-labeled alcohols shows nearly the same activity distribution of formed hydrocarbons, indicating that C-C bonds of incorporated alcohols are not cleaved. Accordingly, the formation of methane is very small.1,3... 

During a study of the biosynthesis of pectin substances, a sensitive micromethod for the assay of pectinesterase activity was developed111 that uses a biosynthetically prepared [14C] methyl-labelled pectin as the substrate after enzymic de-esterification, the substrate remaining is precipitated with an excess of methanol and, after centrifugation, the [14C]methanol present in the supernatant liquor is counted in a liquid scintillation counter in order to assess the pectinesterase activity. 

To this end, the diazoimidazole carboxamide compound 32 was transformed first by methylamine to the methyl-triazene derivative 39, which was reacted with 11 (". -phosgene to give the desired product 40 <2002JME5448>. In another approach, 32 was directly cyclized to the bicyclic product by using 1 C-labeled methyl isocyanate. This route allowed the synthesis of both the C-2-labeled 40 and the (7-methyl-labeled samples 41 <1997JLR371, 2002JME5448> (Scheme 13). 

The Bristol group of Christine Willis, in collaboration with Amersham International, developed a procedure for deuterium (or labeling of nonpolar amino acids." In the chemical steps, a selectively methyl-labeled oxazolidinone is converted first into a 2-methyl carboxylic acid and then lengthened by two carbon atoms without racemization to yield an a-keto methyl ester (Scheme 9). 

The biosynthesis of the p-lactam antibiotic penicillin (Fig. 65), and also of cephalosporin, involves incorporation of L-valine and the question arises as to which of the two diastereotopic terminal methyl groups of the valine occupies which position in the penicillin. (In the case of cephalosporin, the question is as to which methyl group is incorporated into the six-membered ring and which becomes the methylene group of the carbinyl acetate.) The problem has been solved by two groups 65d,141) by synthesis of specifically 13C methyl labeled valine (cf. Fig. 42, and p. 35) which was then biosynthetically incorporated in the antibiotics. The position of the 13C in the resulting antibiotic molecules was determined by 13C NMR spectroscopy. 

C-Methyl-Labeled Milk Proteins for Studies of Protein Interactions and Proteolysis in Milk... 

A simple procedure has been described for preparing 14C-methyl-labeled proteins (1,2). Such derivatives and their fragments still may be detected and measured after the proteins have been denatured or hydrolyzed. In this chapter, we describe experiments that illustrate the use of 14C-methyl-labeled milk proteins to study protein interactions in heated skim milk and to follow enzymic hydrolysis of milk proteins in various milks. 

C-Methyl-Labeled c-Casein. The effect of reductive methylatior on the properties of asi-, / -, and c-caseins was investigated in this labora tory (7). The purified proteins were treated to obtain either 20% oi 60% modification of lysine residues. Electrophoretic mobilities at pE 8.5 or 6.5 of the modified proteins were indistinguishable from those oi the native caseins. 

Methylases specific for each of the four bases of sRNA (97) and for adenine and cytosine of DNA (98) are available. Selective modification of a nucleic acid or its oligonucleotide fragments before digestion with a specific nuclease gives additional dimensions for selective degradation. Use of C-methyl labelled S-adenosylmethionine permits selective isotopic labelling by these enzymes. 

Using 14c, which had just become available, they discovered that 8 of the carbon atoms of heme in nucleated duck erythrocytes are derived from the a-carbon atom of glycine and none from the carboxyl carbon atom. The results of subsequent studies demonstrated that the other 26 carbon atoms of heme can arise from acetate. Moreover, the in methyl-labeled acetate emerged in 24 of these carbons, whereas the in carboxyl-labeled acetate appeared only in the other 2 (Figure 24.341. 

Mutant strains (Pho71, Pho72 and M 402) [50,46,47] which show neither photo-nor chemoresponses lack almost all the methyl-labelled bands in the 70-135 kDa region. 

First of all, the initial oxidation labels (with a —COOH group) the D-glucose unit that contains the free aldehyde group. Next, methylation labels (as —-OCH3) every free —OH group. Finally, upon hydrolysis, the absence of a methoxyl group shows which —OH groups were not free. 

This interconversion was carried out in 88% yield with complete inversion of configuration as judged, for example, by incubation with yeast alcohol dehydrogenase. A similar general route, reductive displacement of a sulfonate ester, was used to prepare chiral-methyl labeled decane (58). In neither case was the chiral purity of the product determined by analysis, but further work by Caspi s group (56, 59) indicated that their material must have had good chiral purity. 

S -adenosyl-L-methionine into pectin (43), -methyl-labelled... 

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