Helical Conformation of Poly-γ-benzyl-L-glutamate

Abstract

RECENTLY, Luzzati et al.¹ and Spach et al.² have suggested that the helical form of poly-γ-benzyl-L-glutamate (PBLG) in dilute solution is that of a 3.0₁₀ helix rather than an α-helix. They reached this conclusion after performing both X-ray diffraction and hydrodynamic experiments on dilute solutions of the polymer in appropriate solvents. They further reviewed the present light-scattering data and concluded that this supported the 3.0₁₀ helical conformation and confirmed the slight flexibility of the helices. They showed that the parameter h, which is the distance between two successive residues projected on to the helix axis or the length of the equivalent rod divided by the degree of polymerization, varied with the molecular weight M and, furthermore, that h approached a value of 2.0 Å as the value of M approached zero. For an α-helix h_M→O should be about 1.5 Å. More recently, Parry and Elliott³ have repeated some of the X-ray diffraction experiments of Luzzati et al., using m-cresol as solvent, and suggest that the conclusions reached by the latter are erroneous, not because of faulty measurements but rather because of incorrect assumptions regarding the packing of the molecule. Parry and Elliott demonstrated that the α-helix is the probable conformat on of the molecule of the PBLG sample investigated.