Remote labeling technique

Remote double labelling techniques have been used successfully in the determination of enzyme KIEs (Kiick, 1991). A variant of this technique was applied to a nonenzymatic reaction by Matsson and co-workers (Axelsson et al., 1990). They determined the primary carbon and secondary deuterium KIEs for the SN2 reaction between methyl iodide and hydroxide ion in 50% dioxane-water at 25°C. The a-carbon KIE was determined by the UC method (Axelsson et al. 1987,1991). In this method, a mixture of substrate molecules labelled with UC (tm = 20.4 min) and 14C is used. The reactants and products... 

Radioactive isotopes are commonly used for competitive KIE measurements in a double-label experiment, yielding kn/kj or ko/kj ratios on kcat/ M- This technique typically utilizes tracer-level radioactivity in the position of interest (primary or secondary) to monitor the transfer of radioactivity from reactant to product, and requires a remote label (e.g. C) in order to measure the conversion of unlabelled substrate to product. As an example, [ring- C(U)]benzyl alcohol and [l- H]benzyl alcohol (Scheme 10.2) can be used to simultaneously measure the primary and a-secondary kn/kj effects in the reaction catalyzed by alcohol dehydrogenase (ADH), as the tracer tritium is incorporated randomly into primary and a-secondary positions [6, 10]. 

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