1SRN:
reference: The refined crystal structure of a fully active semisynthetic ribonuclease at 1.8-A resolution., Martin PD, Doscher MS, Edwards BF, J Biol Chem 1987 Nov 25;262(33):15930-8. PMID: 3680234

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