| Abstract: | The Conformational properties of synthetic S-peptide analogs, in which the residues in the N-terminal sequence 1–6 were progressively deleted or replaced with amino acids of lower helical propensity, were studied by CD. Increasing the concentration of guanidine hydrochloride and decreasing the temperature were found to produce progressive destruction of ordered conformations, in the parallel with the increasing solubility of the peptide unit, while increasing the concentration of trifluoroethanol and decreasing the temperature produced the opposite effect. The maximum helicity determined in the these sets of experiments is found equal to or greater than that determined in the formation of the ribonuclease S′ complexes. With some peptides the maximum value of predicted helical conformation is reached, and the tendency of tertiary structure to reduce the maximum possible helicity is evident. We discuss the validity of the procedure by which conformational information, drawn from measurements in helicogenic solvents, is related to the state in native protein. |
