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

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 1∊,7δ-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 1∊ ,7∊-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. [ABSTRACT FROM AUTHOR]