In order to investigate the roles of Lys1 and Lys7 of RNase A in the enzymatic activity, four S-peptide derivatives were prepared and their abilities to activate S-protein were measured. They are 1-norleucine-S-peptide, 7-norleucine S-peptide, 1,7-di-norleucine-S-peptide, and tri-N-acetyl S-peptide. From the analyses of the relative activity and kinetic parameters of RNase S' derivatives with UpU, UpU greater than p, and UpUpU greater than p, it was concluded that Lys7 of RNase A is a binding site for 3'-phosphate of UpU greater than p and the modification or substitution of Lys1 affects the binding of trinucleotide substrate.

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