Labelled with isotopic

The use of the in vivo labeling methods described above is limited by the fact that the sample must be grown in the presence of the labeling isotopes. In many cases, it is not feasible to perform in vivo metabolic labeling. For example, for human clinical samples it is not possible to perform in vivo labeling and yet it is highly desirable to obtain accurate quantitative information on protein expression levels within these samples. Therefore, robust methods are needed for quantitation of protein levels in the absence of in vivo labeling with isotopes. 

An NMR spectrum shows the types of environment around the nuclei (atoms) and the ratios of these nuclei. Compared with X-ray crystallography, NMR has the advantage of being carried out in concentrated solutions rather than requiring crystal samples. The solution states are more representative of the native environment of receptor proteins. NMR can be used to study ligand-receptor interactions. A receptor protein is labeled with isotopes such as or N, and changes in their spectra when bound with ligands can be monitored. 

Ibritumomab tiuxetan is an anti-CD20 murine monoclonal antibody labeled with isotopic yttrium (90Y) or 11 LIn. The radiation of the isotope provides the major antitumor activity. Ibritumomab is approved for use in patients with relapsed or refractory low-grade, follicular, or -cell non-Hodgkin s lymphoma, including patients with rituximab-refractory follicular disease. It is used in conjunction with rituximab in a two-step therapeutic regimen. 

The alternative approach to the determination of the stereochemistry of hydroxylation )3 to the nitrogen occurring in the biosynthesis of haemanthamine involved the synthesis of stereospecifically labeled tyrosine. Catalytic hydrogenation of suitable acylaminocinnamic acids labeled with isotopic hydrogen in fi position proceeds stereoselectively to furnish an equimolecular mixture of L-(/3i -3H]-and D-[j8 -3H]tyrosine (419) and (420). Enzymic resolution of the racemic amino acid yielded the L and d isomers. The two optically active forms of tyrosine were... 

Benzimidazole derivatives, III, 161 Benzimidazole rule of rotation, I, 21 1,3-Benzodioxan, 8,8 -methyIenebis(6- nitro-), III, xvii Benzoic acid, cellulose esters, I, 320 labelled with isotopic C, III, 231 starch esters, I, 302, 303 —, 2,4-dihydroxy-, effect on conductivity of boric acid, IV, 195 —, 2,4,5-trihydroxy-, effect on conductivity of boric acid, IV, 195 —, 3,4,5-trihydroxy-. See Gallic acid. 

Caproic acid, as glycogenic agent, II, 134 labelled with isotopic C, III, 231 —, deuterio-, metabolism of, II, 152 Caprylic acid, as glycogenic agent, II, 134 labelled with isotopic C, III, 231 metabolism of, II, 152 Carbamic acid, N-phenyl. See Carba-nilic acid. 

Citric acid, II, 148 III, 238, 242, 248 Iahelled with C11, III, 238 labelled with isotopic C, III, 241 from molasses, IV, 336 from sucrose, IV, 322, 324 Citric acid cycle, in carbohydrate oxidation, III, 238... 

Formic acid, cellulose ester, I, 310 from inositol oxidation, III, 52 labelled with C1, III, 237 labelled with isotopic C, III, 231, 232 starch ester, I, 300 from sucrose, IV, 309 Formose, IV, 27... 

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. 

Many of the procedures given above have been utilized for the preparation of mevalonolactone labeled with isotopes of carbon, hydrogen, and oxygen.7-9 Mevalonolactone-14C has been prepared with the label at all six positions l-,7 29 2-,7 143 24 3-,llb 3 -, 203,30 4-,7,183 and 5-14C.19 Preparations of singly and doubly labeled meva-lonolactone-13C have been reported recently 2-,26,31 3-,32 4-,33 3, 4-,7,183 3,4-,26,33b and 4,5-13C.34 The procedure described here26 for the preparation of mevalonolactone-2-13C is both convenient and economical compared to the usual Reformatsky methods since acetic acid-2-13C is utilized directly in the condensation reaction, rather than methyl or ethyl bromoacetate. The overall yield of mevalonolactone-2-13C is 46-52% based on acetic acid-2-13C. 

Three 5a-androst-6-ene derivatives have been recorded as intermediates for labelling with isotopic hydrogen.50 Reaction of 3/3-acetoxyandrost-5-en-17-one with N-bromosuccinimide-perchloric acid followed by oxidation of the intermediate 5,6-bromohydrin gave the diketone (133 R1 = Br, R2 = H), which on treatment with... 

SUGARS SPECIFICALLY LABELED WITH ISOTOPES OF HYDROGEN ... 

IX. Tables of Known Sugars Specifically Labeled with Isotopes of Hydrogen.. 181... 

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