Magnesium isotopically labelled

Bohn, T., Walczyk, T., Davidsson, L., Pritzkow, W., Klingbeil, P., Vogl, J., and Hurrell, R.F. (2004) Comparison of urinary monitoring, faecal monitoring and erythrocyte analysis of stable isotope labels to determine magnesium absorption in human subjects. Br. J. Nutr., 91 (1), 113-120. 

The intravenous administration of a second isotopic label can also be used to assess true absorption of the oral isotopic labels for elements that are excreted via the kidneys, such as calcium and magnesium. As in plasma appearance studies, the intravenous label serves as a reference dose. When the second label is infused or injected slowly following administration of the labeled test meal, both labels appear in parallel in serum/plasma. Some of the circulating labels, however, are excreted via the kidneys, during which the amount ratio of the two labels in blood should ideally be preserved. If this is so, a single spot urine sample can be used, at least in theory, to determine the amount ratio of the two labels in serum. As the intravenous dose is known, this ratio can then be converted into the amount of oral label absorbed. As for most stable isotope techniques, this method was originally developed for radiotracers [31] and adapted for stable isotopes in the 1980s [32]. 

The stereospecific conversion of menthyl arenesulphinates into chiral aryl methyl sulphoxides may also be achieved by means of methyllithium . The reaction of methyllithium with diastereoisomerically or enantiomerically pure arenesulph-inamides 283 was found to give optically active aryl methyl sulphoxides 284 (equation 156). The preparation of optically active sulphoxides 285 and 286, which are chiral by virtue of isotopic substitution (H - D and - respectively), involves the reaction of the appropriate non-labelled menthyl sulphinates with fully deuteriated methyl magnesium iodide (equation 157) and with benzylmagnesium chloride prepared from benzyl chloride labelled with carbon (equation 158). 

Magnesium perchlorate, as catalyst in acetylation of starch, I, 289 Maleic acid,.dihydroxy-, II, 96 III, 149 Malic acid, III, 238, 241 IV, 85 labelled with isotopic C, III, 140, 249 Malonic acid, II, 155 III, 238 protection of enzyme by, V, 54 Maltamylase. See under Amylases. Maltase, IV, 25, 30. See also a-Glucosi-dase. 

Although isotope exchange by virtue of its simplicity and ability to form compounds of high specific activity is the method of choice for the labelling of tautomeric thiols, a synthetic method is often better suited to other thiols. For example, heating a-toluenethiol with sulphur- S in benzene at 135-140°C for 6-12 h, yields ct-toluenethiol- S with a specific activity of only 2-9%. However, the synthesis of the compound from benzyl-magnesium chloride and sulphur- S yields a-toluenethiol- S... 

Extracts of acetone-dried pigeon liver catalyze the synthesis of GSH from glutamic acid, cysteine, and glycine provided magnesium ions and ATP are added (2). Marked stimulation of sjmthesis is provided by potassium ions. After the removal of hydrolytic enzymes from the crude extract, a net synthesis of GSH can be demonstrated by means of the glyoxalase assay (2). The close correspondence between the values obtained by the glyoxalase assay and by the isotopic technique shows that in this system the incorporation of a labeled amino acid into GSH is a measure of de novo synthesis. 

Schwartz, R., Grunes, D.L., Wentworth, R.A., and Wien, E.M. (1980) Magnesium absorption from leafy vegetables intrinsically labeled with the stable isotope Mg. J. Nutr., 110, 1365-1371. 

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