2SGA:
reference: Electron density calculations as an extension of protein structure refinement. Streptomyces griseus protease A at 1.5 A resolution., Moult J, Sussman F, James MN, J Mol Biol 1985 Apr 20;182(4):555-66. PMID: 3892015

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).