CONFORMATIONAL STUDIES OF A SERIES OF OVERLAPPING PEPTIDES FROM RIBONUCLEASE AND THEIR RELATIONSHIP TO PROTEIN STRUCTURE

Overlapping peptides comprising amino acid residues 1-8, 1-13 (C-peptide), 1-15, and 1-20 (S-peptide) from the amino-terminal region of ribonuclease A were isolated. Circular dichroism spectra in ion-free water and dilute Na2SO4 at 26 and 1° showed that the three longer peptides are partially helical and that the helicity increased moderately in water at low temperatures but markedly in salt at low temperatures. Residues 2-12 are known to be helical in the X-ray crystal structure of ribonuclease. Molar ellipticities of the three longer peptides at 224 nm in 0.033 m Na2SO4 were essentially the same at low temperature, thus supporting the concept that the 1-12 region tends to be helical in the isolated peptide as in the intact protein. The 14-20 region is not helical. Such a series of overlapping peptides constitutes a model system for the study of the initiation of folding by short-range interactions. © 1969, American Chemical Society. All rights reserved.