Husain S S, Lowe G
Biochem J. 1968 Aug;108(5):855-9. doi: 10.1042/bj1080855.
Papain was irreversibly inhibited by 1,3-dibromoacetone, a reagent designed to react first with the active-site cysteine residue and subsequently with a second nucleophile. The molecular weight of the inhibited enzyme was indistinguishable from that of papain itself, and no evidence of dimeric or oligomeric species was found. The optical-rotatory-dispersion curves of chloroacetone-inhibited papain and 1,3-dibromoacetone-inhibited papain were essentially similar. Amino acid analysis of the 1,3-dibromo[2-(14)C]acetone-inhibited enzyme and the performic acid-oxidized material clearly showed that a cysteine and histidine residue had been alkylated through the thiol and N-1 of the imidazole group respectively. These groups must therefore be within 5å of each other in the tertiary structure of papain. Possible mechanistic implications are briefly discussed.
木瓜蛋白酶被1,3 - 二溴丙酮不可逆地抑制,1,3 - 二溴丙酮是一种设计用于首先与活性位点半胱氨酸残基反应,随后再与第二个亲核试剂反应的试剂。被抑制的酶的分子量与木瓜蛋白酶本身的分子量没有区别,并且未发现二聚体或寡聚体形式的证据。氯丙酮抑制的木瓜蛋白酶和1,3 - 二溴丙酮抑制的木瓜蛋白酶的旋光色散曲线基本相似。对1,3 - 二溴[2 - (14)C]丙酮抑制的酶和过甲酸氧化的物质进行氨基酸分析清楚地表明,一个半胱氨酸和一个组氨酸残基分别通过硫醇和咪唑基团的N - 1被烷基化。因此,在木瓜蛋白酶的三级结构中,这些基团彼此之间的距离必定在5埃以内。文中简要讨论了可能的机制含义。