CONFORMATIONAL STABILITY OF A SNAKE CARDIOTOXIN

A snake cardiotoxin from the venom of the Formosan cobra, Naja naja atra, is a basic polypeptide. The protein can be denatured in 6.0 M guanidine hydrochloride or at elevated temperatures. Its conformation remains virtually the same in solvents of lower polarity than water such as 1, 2‐ethanediol or 1‐propanol and 1, 2‐ethanediol (1:1 v/v). The circular dichroism spectrum is atypical in water in that the peptide chromophores show a small negative CD band at 214 nm and a large positive one at 195 nm. To some extent the CD pattern resembles that of the β‐form but differs in specific positions and magnitudes. Considering that the theoretical CD of the reverse β‐bend and the characteristics of model polypeptides in β‐form manifest a similar pattern, we suggest that cobra cardiotoxin is rich in β structure including β pleated‐sheets and β reverseturns.