Carey P R, Ozaki Y, Storer A C
Biochem Biophys Res Commun. 1983 Dec 28;117(3):725-31. doi: 10.1016/0006-291x(83)91657-1.
The resonance Raman spectra of several enzyme-substrate intermediates of papain, chymopapain, ficin and bromelain are reported. The intermediates are dithioacyl enzymes formed during the catalyzed hydrolysis of N-acylglycine thionoester substrates. Interpretation of the resonance Raman spectra allows us to compare, for the first time, the substrate geometries in a series of functioning intermediates from different enzymes. The substrates assume essentially identical conformations for papain, chymopapain and ficin and a similar, but not identical, conformation in the active site of bromelain. Each dithioacyl enzyme population appears to be made up of a single homogeneous conformational state. This state has been characterised in earlier studies of dithioacyl papains. It is designated as conformer B and is characterized by an attractive contact between the substrate's glycinic N atom and the active site cysteine S atom. It is now apparent that conformer B is of general significance in the mechanism of cysteine proteases.
本文报道了木瓜蛋白酶、凝乳木瓜蛋白酶、无花果蛋白酶和菠萝蛋白酶几种酶-底物中间体的共振拉曼光谱。这些中间体是在N-酰基甘氨酸硫代酯底物催化水解过程中形成的二硫代酰基酶。共振拉曼光谱的解析使我们首次能够比较来自不同酶的一系列功能中间体中的底物几何结构。木瓜蛋白酶、凝乳木瓜蛋白酶和无花果蛋白酶的底物具有基本相同的构象，而在菠萝蛋白酶的活性位点中底物具有相似但不完全相同的构象。每个二硫代酰基酶群体似乎都由单一的均匀构象状态组成。这种状态在二硫代酰基木瓜蛋白酶的早期研究中已有描述。它被指定为构象体B，其特征是底物的甘氨酸N原子与活性位点半胱氨酸S原子之间存在吸引性接触。现在很明显，构象体B在半胱氨酸蛋白酶的机制中具有普遍意义。
