Multiple isomorphous replacement

Multiple isomorphous replacement or MIR is, historically speaking, the most common approach to solving the phase problem in X-ray crystallography. For protein crystals this method is conducted by soaking the crystal of a sample to be analyzed with a heavy atom solution or co-crystallization with the heavy atom. The addition of the heavy atom should not affect the crystal formation or unit cell dimensions in comparison to its native form, hence, they should be isomorphic.