Abstract
AbstractCircular dichroism (CD) of soybean trypsin inhibitor (STI, the „KUNITZ inhibitor”︁)and some of its derivatives was studied in the spectral region of 185 to 320 mμ. Acetylation and succinylation, as well as denaturation with 6 M guanidine hydrochloride resulted in small changes in the CD spectra. In strongly acid solutions at pH 1.8 to 2.0 was observed a decrease of the amplitude of the positive COTTON effect at 226 mμ and a shift of this band to 230 mμ. Remarkable changes were observed in the CD spectra after cleavage of the disulfide bonds of STI either by reduction or sulfitolysis. The positive band at 226 mμ thereby disappeared, the negative bands around 240–300 mμ were modified and the amplitude of the strong negative COTTON effect at 200 mμ was diminished by the cleavage of the disulfide bonds. Reconstitution of the disulfide bonds lead to CD patterns resembling those of the native protein. The antitryptic activity of all chemically modified samples was significantly lowered.
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