Examples of electron density
Figures from Bernhard Rupp's book "Biomolecular Crystallography" (with permission by the author)
There is more material (all figures, citations, tutorials) at the book's overview page.
You can see the full-size, high-resolution figure by clicking on it.
Cis-peptide bond and its electron density
Covalently modified residues
Covalent binding of ligands
Additives mediating intermolecular contacts
Heavy-atom derivatization of a protein
The trimeric bacterial outer membrane protein OprP
Chemically modified lysine residue (Dimethyllysine)
Glycosylated residues stabilizing homodimer
Uranium-atom solution and Fourier truncation ripples
Solvent molecules (water, MPD, Mg2+)
Split side-chain conformations
Se-Met residues and chloride ion
