THE SOLUTION PROPERTIES AND CONFIGURATIONS OF A POLYAMPHOLYTIC POLYPEPTIDE: COPOLY-L-LYSINE-L-GLUTAMIC ACID

Abstract

Equimolar copolymers of L-lysine and L-glutamic acid were prepared and characterized. Equilibrium behavior as a function of pH, apparent metastable states and behavior in organic solvents were studied. The copolymers with molecular weights of about 40,000 were found to exhibit the [alpha]-helical configuration to the extent of 15% in neutral 0.15 [image] NaCl. At pH 4 the amount increases to 50% and decreases to zero at pH 12 or upon removal of the NaCl. Two apparent metastable states were observed in copolymers that had no exposure to alkaline pH. The addition of urea causes denaturation of the copolymers similar to that occurring with proteins. In chlorethanol the polypeptide is completely helical but on the addition of trifluoroacetic acid a transition to the randomly coiled form takes place in a manner very similar to proteins such as ovalbumin. Thus, the copolymer apparently has a distribution of more and less stable helix regions comparable to proteins.