Methionine doubly labeled

The use of methionine doubly labeled in the methyl group was subsequently extended to experiments with higher plants by Byerrum, Ball, and their co-workers. It was shown that the methyl group of methionine was a precursor of the N-methyl of nicotine in tobacco (Dewey et al., 1954), the methyl ether groups of lignin in barley and tobacco (Byerrum et al., 1954), and the methyl esters of pectinic acid in radish (Sato et ah, 1957). In none of these methylations was the deuterium ratio in... 

Stable isotope methodology has been applied to the study of the biosynthesis of madumycin II (A2315A, 92) in Actinoplanes philippensis (60, 64). As with virginiamycin Ml (90), carbons 2, 26, 27, and 28 were found to be derived from valine, C-29 from methionine, C-3 to C-6 from acetate, N-7, C-8, and C-9 from glycine, carbons 10 to 17 and C-31 from acetate, and N-18, C-19, C-20, 0-21, C-32, and 0-34 from serine. The origin of the D-alanine residue, N-23, C-24, C-25, C-35, and 0-36, was of particular interest in this study. No incorporation of DL-[U-13C]serine was observed in the alanine portion of the molecule, eliminating the intermediacy of the a,(3-dehydro alanine unit 101 derivable from the acylserine precursor 100. This was corroborated by the observed incorporation into the molecule of intact doubly labeled L-[3-l3C,3,3,3-2H]alanine. dl-[1-l4C]Alanine was also efficiently incorporated. These results and those from de-... 

The biogenesis of nicotine has been studied in the plant with the aid of radioactive tracers. It was first shown that sodium formate is a precursor of the iV-methyl group of nicotine, but that methionine is a more immediate precursor since when these substances labeled with C are fed to the plant, the yield in radioactivity is greater with methionine than with formate (44). It was concluded that the methy-lation by methionine involved a true transmethylation and that the methyl group was not transferred via an intermediate oxidation to formate (44). This view found support in the results of an experiment involving the use of methionine with its methyl group doubly labeled with and deuterium. In this experiment, the ratio of the and... 

An enzyme preparation from jack bean meal will transfer a methyl group from S-methylmethionine 167 to homocysteine 148 to yield 2 mol of methionine 149. Use of the doubly labeled compounds 166a and 166b, separated by the method of Cornforth et al. (160), conversion to the (Cs, Sj)- and (Cj, Ss)-isomers of methylmethionine 167a and 167b, and incubation with the enzyme, allowed mass spectrometry to be used to show that the pro-R methyl group of S-methylmethionine is transferred to L-homocysteine 148 (161,162), as shown in Scheme 52. 

This was confirmed by feeding methionine in which tlie metiiyl group was doubly labeled with and D. The ratio of D to C " in the methyl groups of the isolated choline was the same as in the methionine. However, it should be noted that it is now known that methyl groups can be formed by reduction of such single-carbon entities as formaldehyde and formate. 

Studies with methionine labeled in the methyl group with both and deuterium have been carried out by Melville, Ludwig, Inamine, and Rachele (1959). Ergothioneine synthesized by N. crassa from this doubly labeled methionine was degraded to trimethylamine, and the C and D content of this compound was compared with the isotope concentrations in the methionine methyl group. The results (Table VIII) demonstrate an... 

It was found that the dilution of and D could be markedly reduced by using a methionine-less mutant of N. crassa. Repetition of the experiment with this mutant, grown in the presence of doubly labeled meiliionine, yielded ergothioneine in which the trimethylammonium moiety was heavily labeled with both and D (Table IX). Since the specific activities of the and D in the trimethylamine are significantly greater than two-thirds... 

As stated, sulfur nucleophiles are expected to labilize amines in a tram position and the isolation of the platinum—methionine metabolite is further evidence that these reactions occur in vivo. Evidence for amine displacement, even of chelated ethylenediamine, has also been obtained from solution studies with methionine-containing peptides and RNase A [117]. In connection with these results the dissociation of doubly labelled [PtCl2(en)] (on the Pt and C) in vivo has been confirmed, negating earlier results [118]. 

Sometimes double or even triple labelling can be useful. Some poner-ine ants have dimethyl disulphide in their mandibular glands. Crewe and Ross Insect Biochemistry, 1975, 5,839) used doubly labelled methionine to show that the methyl and sulphur were incorporated together into the dimethyl disulphide by Paltothyreus tarsatus ants (Figure 5.5). 

The ponerine ant, Paltothyreus tarsatus, produces various alkyl sulfides in its mandibular glands (471, 472). With the use of doubly labelled methionine, it has been established that the CHs-S-group is incorporated intact but the origin of the third sulfur atom in dimethyl trisulfide remains unknown (473, 474). 

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