A STATISTICAL THERMODYNAMIC STUDY ON THE CONFORMATIONAL TRANSITION OFOLIGOPEPTIDE MULTIMER

The conformational transition of oligopeptide multimer, -(HPPHPPP)n-, is studied (H:hydrophobic amino acid, P:hydrophilic amino acid). The h elix/coil transitions are detected in the multimer. The transition dep ends on the number of amino acid in the sequence, the concentration of the oligopeptide, and temperature which affects helix stability const ant (xi) and hydrophobic interaction parameter (w(j)) In the thermodyn amic equilibrium system jA-->A(j) (where A stands for oligopeptide mon omer), Skolnick et al., explained helix/coil transition of dimer by th e matrix method using Zimm-Bragg parameters xi and sigma (helix initia tion constant). But the matrix method do not fully explain dangling H- bond effects which are important in oligopeptide systems. In this stud y we propose a general theory of conformational transitions of oligope ptides in which dimer, trimer, or higher multimer coexists. The partit ion of trimer is derived by using zipper model which account for dangl ing H-bond effects. The transitions of multimers which have crosslinke d S-S bonds or long chains do not occur, because they keep always heli cal structures. The transitions due to the concentration of the oligop eptides are steeper than those due to the chain length or temperature.