Relation between Structure and Function in Some Partially Synthetic Ribonucleases S′

Abstract
Some analogues have been prepared of S‐peptide, the peptide obtained together with S‐protein from subtilisin‐modified beef pancreatic RNase A. The syntheses are described of [Orn10, Asn14]‐S‐peptide and 1ɛ, 7ɛ,10δ‐triguanidino‐[Orn10, Asn14]‐S‐peptide. The S‐peptide analogues are able to activate S‐protein at the level of the parent [Orn10]‐S‐peptide and 1ɛ,7ɛ‐diguanidino‐S‐peptide respectively, although at high peptide‐to‐protein molar ratios. After their recombination with S‐protein the buried character of Tyr‐25 was restored, as judged from difference absorption and circular dichroism spectra in the near‐ultraviolet region. These findings indicate that the asparaginyl residue is a possible naturally occurring substituent in the RNase A sequences whose state of amidation in position 14 has not yet been defined.