Evidence for histidine in the active site of papain.
Evidence for histidine in the active site of papain.
复制标题
木瓜蛋白酶活性位点中组氨酸的证据。
作者：
S. Husain;G. Lowe
木瓜蛋白酶被不可逆地抑制1，3-二溴丙酮，一种试剂，旨在首先与活性位点的半胱氨酸残基，随后与第二亲核试剂反应。被抑制酶的分子量与木瓜蛋白酶本身的分子量难以区分，也没有发现二聚体或寡聚体的证据。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。1，3-二溴[2-（14）C]丙酮抑制的酶和过甲酸氧化的材料的氨基酸分析清楚地表明，半胱氨酸和组氨酸残基已分别通过咪唑基团的硫醇和N-1烷基化。因此，在木瓜蛋白酶的三级结构中，这些基团必须彼此在5 μ m以内。可能的机制的影响进行了简要讨论。
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.