Crystallographic Study of Biomacromolecules

The following steps are typically used in the crystallographic study of biomacromolecules  

2 Preparation of isomorphous heavy-atom derivatives. The multiple isomorphous replacement technique has been commonly used to solve biomacromolecular structures. It requires the parent crystal and at least two heavy-atom derivatized crystals identical in space group and molecular structure. The common technique uses reagents containing heavy atoms and allows them to diffuse into the crystal. 

3 Determination of X-ray diffraction patterns for parent and isomorpous crystals. The spacing of the indexed reflections is inversely proportional to the lengths of the crystal unit cell. Since the relative spacing between reflections is needed for determining the lengths of the unit cell axes, it is important to obtain an undistorted diffraction pattern. Each reflection in the diffraction pattern can be assigned to a unique set of Miller indices from the Laue conditions for diffraction. The pattern is indexed in term of the Miller indices. 

4 Determination of structure factors, location of heavy atoms for isomorpous crystals. The electron density distribution of the heavy-atom isomorphous crystal is the sum of the electron densities of the parent crystal and of the heavy-atom substituents, i.e.  

5 Estimation of phases of the structure factor. Both the phase and amplitude of the contribution of the heavy atom to the structure factor are computed to yield Fh. 

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