Totally synthetic crystalline ribonuclease A

Improved chemical synthesis of bovine pancreatic ribonuclease (RNase) A was achieved by applying a new deprotecting procedure with trifluoromethanesulfonic acid–thioanisole in combination with a modified air‐oxidation procedure with glutathione for the disulfide formation. After purifications by affinity chromatography, followed by ion‐exchange chromatography, a protein with the full enzymatic activity was obtained and subsequently crystallized from aqueous ethanol according to Kunitz. A totally synthetic enzyme with full RNase A activity was thus obtained in a crystalline form for the first time.