STUDIES ON CONFORMATION OF RIBONUCLEASE S-PEPTIDE

Ribonuclease S-peptide is the amino-terminal eicosapeptide segment of bovine pancreatic ribonuclease A (i.e., residues 1-20). In the intact ribonuclease molecule a large portion of this segment is found to be helical (Kartha, G., Bello, J., and Harker, D. (1967), Nature 213, 862; Wyckoff, H. W., Hardman, K. D., Allewell, N. M., Inagami, T., Johnson, L. N., and Richards, J. M. (1967), J. Biol. C hem 242, 3984). The circular dichroism of S-peptide in dilute aqueous solution has been measured over a broad range of pH (1-11.5) and temperature (4-79°). These measurements show negative circular dichroism peaks near 200 and 225 mμ which indicate the presence of both helical and random coil structures in S-peptide throughout this range of conditions. In 5 M guanidine hydrochloride the peptide behaves as a random coil whereas 2-chloroethanol induces a high degree of helicity. These results are taken to indicate that, in the course of its conformational fluctuations, S-peptide often assumes a structure which is similar to that of the amino-terminal segment of intact ribonuclease. © 1968, American Chemical Society. All rights reserved.