PARAMETERS OF HELIX-COIL TRANSITION THEORY FOR ALANINE-BASED PEPTIDES OF VARYING CHAIN LENGTHS IN WATER

Thermal unfolding curves have been measured for a series of short alanine-based peptides that contain repeating sequences and varying chain lengths. Standard helix-coil theory successfully fits the observed transition curves, even for these short peptides. The results provide values for sigma, the helix nucleation constant, DELTA-H-degrees, the enthalpy change on helix formation, and for s(0-degrees-C), the average helix propagation parameter at 0-degrees-C. The enthalpy change agrees with the value determined calorimetrically. The success of helix-coil theory in describing the unfolding transitions of short peptides in water indicates that helical propensities, or s values, can be determined from substitution experiments in short alanine-based peptides.