For solution of the macromolecular phase problem, the most commonly used methods (multiple isomorphous replacement (MIR) and multiple wavelength anomalous dispersion (MAD)) still involve the incorporation of heavy atoms into protein crystals. Finding such derivatives using the classical "trial-and-error" approach is - after crystallization - the second major bottle neck in the determination of the 3D structure of bio-macromolecules.

Brominated and Iodinated ATP and GTP analogs, however, provide an alternative method that allows rational incorporation of heavy atoms into a large number of physiologically relevant enzymes (see also the Macromolecular Crystallography Section for more details and more products).

Furthermore, the availability of a suitable leaving group such as iodine, opens new ways to a straightforward introduction of functional groups for the synthesis of novel nucleotide analogs.