Electron microscopic observations on the super helical structure of synthetic polypeptide

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Abstract
A study of the super helical structure of synthetic polypeptides, such as poly‐γ‐benzyl‐D (or L)‐glutamate (PBDG or PBLG) was carried out. The PEG was dissolved in dimethylformamide (DMF). The solution was either allowed to remain at room temperature for a long time or poured into some fatty acid, such as formic acid, acetic acid, propionic acid, or caprylic acid. Whether the polymer precipitated slowly or rapidly depended upon the aging of the solution or the nature of the acid used. The precipitated gels revealed the coiled coil fibrils, but the feature and degree of coiling varied, depending upon the length of aging or the nature of the acid used for precipitation. After a short aging of the solution, there was no helical structure in the gels. After long aging, very fine‐coiled coil macrofibrils or small spindle‐like fibrils were obtained. The macrofibrils consisted of the spindle‐like fibrils which in turn consisted of microfibrils (diam. 60–70A.). When using the fatty acid precipitation very fine to medium fine super helices were obtained. Extremely fine super helices were obtained in propionic acid. In these gels the PBG chains have an α‐helical conformation. When PMLG–DCA solution was stored for a long time, another type of precipitation was obtained, one giving evidence of so‐called cross‐β crystallization and no coiled coil fibrils. The precipitation of cross‐β fibrils was obtained when the concentration of the solution was above 8%.