How to get the magic triangle and the MAD triangle into your protein crystal.

The magic triangle 5-amino-2,4,6-triiodoisophthalic acid (I3C) and the MAD triangle 5-amino-2,4,6-tribromoisophthalic acid (B3C) are two representatives of a novel class of compounds that combine heavy atoms for experimental phasing with functional groups for protein interactions. These compounds are readily available and provide easy access to experimental phasing. The preparation of stock solutions and the incorporation of the compounds into protein crystals are discussed. As an example of incorporation via cocrystallization, the incorporation of B3C into bovine trypsin, resulting in a single site with high occupancy, is described.