title: Optical activity and conformation of cobra neurotoxin.
abstract: Cobra neurotoxin from Formosan cobra (Naja naja atra) venom is a compact globular protein having an intrinsic viscosity of 4.5 mL/g. The protein is stable in 7.5 M urea but can be denatured in 4.1 M guanidine hydrochloride or at elevated temperature (above 70 degrees C). Its conformation remains virtually the same in solvents of lower polarity than water such as 1,2-ethanediol or a mixed solvent of 1-propanol-1,2-ethanediol-water (5:1:1 by volume). The circular dichroism spectrum is "atypical" in water in that the peptide chromophores show a small negative circular dichroic (CD) band at 215 nm, a large positive one at 199 nm, and another large negative one below 190 nm. The CD pattern resembles to some extent that of a beta form but differs in both positions and magnitudes from the latter. It agrees qualitatively with the theoretical calculations of the reverse beta bends, suggesting that cobra toxin contains a considerable amount of beta turns and possibly a mixture of beta form and beta turns.
mesh_terms: D000433:1-Propanol; D002942:Circular Dichroism; D005026:Ethylene Glycols; D006146:Guanidines; D006358:Hot Temperature; D009904:Optical Rotation; D011487:Protein Conformation; D012910:Snake Venoms / Q000032:analysis; D014508:Urea
chemical_list: D005026:Ethylene Glycols; D006146:Guanidines; D012910:Snake Venoms; D014508:Urea; D000433:1-Propanol