The detection of intermediates in enzyme-catalyzed reactions can be accomplished by several techniques. For those intermediates which do not have easily observed electronic spectra, use can be made of isotope exchange phenomena if the chemistry of the reaction is appropriate. Recently, the technique of positional isotope exchange (intramolecular isotopic scrambling) has been used to study several reactions which have been thought to involve high-energy intermediates in their mechanisms. A review of some of these reactions and the limitations of the method are presented in this article.
