Tryptophan(Trp) in cysteine proteinase inhibitor(CPI) from wheat seed was modified with N Bromosuccinimide(NBS). The data showed that there is one Trp in CPI, the modified CPI lost its inhibitory activity on papain completely.

• 用N－溴代丁烯二酰亚胺修饰小麦巯基蛋白酶抑制剂（CPI），计算出CPI分子内有一个色氨酸残基被修饰，修饰的CPI对木瓜蛋白酶的抑制活性全部丧失，表明色氨酸对CPI的活性非常重要，是分子保持抑制活性所必需的；