THERMODYNAMICS OF HELIX-COIL TRANSITIONS STUDIED BY MULTICANONICAL ALGORITHMS

Thermodynamics of helix-coil transitions in amino acid homo-oligomers are studied by the recently proposed multicanonical algorithms. Homo-o ligomers of length 10 are considered for three characteristic amino ac ids, alanine (helix former), valine (helix indifferent), and glycine ( helix breaker). For alanine other lengths (15 and 20) are also conside red in order to examine the length dependence. From one multicanonical production run with completely random initial conformations, we have obtained the lowest-energy conformations and various thermodynamic qua ntities (average helicity, Zimm-Bragg s and sigma parameters, free ene rgy differences between helix and coil states, etc.) as functions of t emperature. The results confirm the fact that alanine is helix-forming , valine is helix-indifferent, and glycine is helix-breaking.