CONFORMATIONAL STABILITY OF A SNAKE CARDIOTOXIN

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Abstract
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 vol/vol). The circular dichroism [CD] 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 .beta.-form, but differs in specific positions and magnitudes. Considering that the theoretical CD of the reverse .beta.-bend and the characteristics of model polypeptides in .beta.-form manifest a similar pattern, cobra cardiotoxin is probably rich in .beta. structure including .beta. pleated-sheets and .beta. reverse-turns.