Incorporating isotopically labeled

Metabolically incorporate isotopic label into either control or treatment cell cultures for 5 or 6 population doublings... 

Hunt and Morris [29] have incorporated isotopic labeling into the technique in order to aid in the interpretation of the resulting spectra. By treating the sample with a 1 1 mixture of CH3OH/CD3OH plus HCl, all... 

Devising a synthetic route incorporating isotope labels into small organic molecules must naturally take into account the technical feasibility of introducing the isotopic labels into the final compound from commercially available... 

When benzoic acid is allowed to stand in water enriched in isotopic label becomes incorporated into the benzoic acid The reaction is cat alyzed by acids Suggest an explanation for this observation... 

Mechanism I was ruled out by an isotopic labeling experiment. The mixed anhydride of salicylic acid and acetic acid is an intermediate if nucleophilic catalysis occurs by mechanism 1. This molecule is known to hydrolyze in water with about 25% incorporation of solvent water into the salicylic acid. 

The oxygen in water is primarily (99.8%) l60, but water enriched with the heavy isotope, 80 is also available. When an aldehyde or ketone is dissolved in 180-enriched water, the isotopic label becomes incorporated into the carbonyl group. Explain. 

When a carboxylic acid is dissolved in isotopically labeled water, the label rapidly becomes incorporated into both oxygen atoms of the carboxylic acid. Explain. 

Problem 29.5 Evidence for the role of acetate in fatty-acid biosynthesis comes from isotope-labeling experiments. If acetate labeled with 13C in the methyl group ( CFtyCC H) were incorporated into fatty acids, at what positions in the fatty-acid chain would you expect the, 3C label to appear ... 

Yeom and Frei [96] showed that irradiation at 266 nm of TS-1 loaded with CO and CH3OH gas at 173 K gave methyl formate as the main product. The photoreaction was monitored in situ by FT-IR spectroscopy and was attributed to reduction of CO at LMCT-excited framework Ti centers (see Sect. 3.2) under concurrent oxidation of methanol. Infrared product analysis based on experiments with isotopically labeled molecules revealed that carbon monoxide is incorporated into the ester as a carbonyl moiety. The authors proposed that CO is photoreduced by transient Ti + to HCO radical in the primary redox step. This finding opens up the possibility for synthetic chemistry of carbon monoxide in transition metal materials by photoactivation of framework metal centers. 

Both absolute quantitation and relative quantitation of species in mixtures is of interest in some circumstances. Quantitation in a 5-minute analysis can be achieved by addition of an internal standard, ideally the target microorganism grown in special media to incorporate heavy isotopes92-95 and determination of the relative peak heights of pairs of proteins from the analyte and the standard. Isotope-labeled proteins or peptides, selected to match proteins or peptides characteristic of target microorganisms, can also serve as internal standards for isotope ratio measurement. The addition of unmatched proteins or peptides is less reliable for either ESI or MALDI measurements because of unpredictable suppression in the variable mixture. 

Veenstra, T. D. Martinovic, S. Anderson, G. A. Pasa-Tolic, L. Smith, R. D. Pro-teome analysis using selective incorporation of isotopically labeled amino acids. /. Am. Soc. Mass Spectrom. 2000,11, 78-82. 

A wide range of other isotopic labels, e.g. 3H (or T), 13C, I4C, 15N, 32P, 35S, 37C1, 1311, etc., have also been used to provide important mechanistic information. The major difficulties encountered in such labelling studies have always been (a) ensuring that the label is incorporated only into the desired position(s) in the test compound and (b) finding exactly where the label has gone to in the product(s) after the reaction being studied has taken place. 

The proteomics research of a number of scientists was described in a C E News report of the 2001 Pittcon meeting.10 One group, that of Catherine Fenselau at the University of Maryland, has studied a new method for proteolytic stable isotope labeling to provide quantitative and concurrent comparisons between individual proteins from two entire proteome pools.11 Two lsO atoms are incorporated into the... 

Until recently, cell-free protein expression (also sometimes erroneously named in vitro protein expression) did not exhibit the productivity required for preparation of NMR samples, especially considering the high cost of using isotopically labeled starting material. Rather, it was exclusively used as an analytical tool that served to verify correct cloning or to study promotor sites. Because of the very low yields, detection of the expressed product usually required incorporation of a radioactive label (usually via 35S-methionine). 

DNA can be isotopically labeled not only using the enzymatic approach mentioned above but also using solid-state phosphoamidite synthesis. This methodology, developed in the 1980 s and modified recently to incorporate the isotope labels, is of advantage when residue- and site-specific patterns of 13C and/or 15N and/or 2H labeling is needed [3]. 

Most of the early methods for assigning isotopically labeled nucleic acids were developed using RNA samples, since 13C and 15N isotopes can be incorporated in RNA more easily than in DNA. While most of the magnetization transfer pathways in RNA and DNA are the same, the latter contains thymine rather than uracil. To remove the ambiguity of intra- and inter-residue H6-CH3 peak assignment in thymine, the HCCCH through-bond method was proposed [51] as a more sensitive alternative to NOE or ROE. 

Of course, isotope filtering is not restricted to such binary systems, but can also be applied to multicomponent systems such as multiprotein complexes, or one or more ligands bound to proteins or protein complexes. It is also conceivable to construct single molecules from sections with different isotopic labeling in order to selectively observe one part by isotopic filtering. However, in these cases a specific synthetic approach has to be designed to allow for efficient incorporation of the isotope labels into the appropriate parts only (for example, by fragment condensation or inteins see also Chapt. 1) [5]. 

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