Dubois T, Jacquet A, Schnek A G, Looze Y
Laboratoire de Chimie Générale I, Université de Bruxelles.
Biol Chem Hoppe Seyler. 1988 Aug;369(8):733-40. doi: 10.1515/bchm3.1988.369.2.733.
Three thiol proteinases, namely papain, chymopapain and proteinase omega were purified to homogeneity from the latex of Carica papaya L. During the purification procedure, the thiol function of the cysteinyl residues were protected either as mixed disulfides with cysteamine or 2-thiopyridone or as S-sulphenylthiosulfate derivative or after blocking with p-chloromercuribenzoic acid. In marked contrast with earlier publications, chymopapain also was found to be a monothiol proteinase as papain and proteinase omega. The active sites of chymopapain and proteinase omega could not be distinguished from that of papain neither by the analysis of the pH dependence of kcat/Km nor by the examination of the pH dependence of the fluorescence emission spectra.
从番木瓜（Carica papaya L.）的乳汁中纯化出了三种巯基蛋白酶，即木瓜蛋白酶、凝乳蛋白酶和蛋白酶ω，使其达到了均一性。在纯化过程中，半胱氨酰残基的巯基功能通过与半胱胺或2-硫代吡啶酮形成混合二硫键、作为S-亚磺酰硫代硫酸盐衍生物或用对氯汞苯甲酸封闭后得到保护。与早期的出版物形成显著对比的是，凝乳蛋白酶也被发现与木瓜蛋白酶和蛋白酶ω一样是单巯基蛋白酶。通过分析kcat/Km对pH的依赖性或通过检查荧光发射光谱对pH的依赖性，凝乳蛋白酶和蛋白酶ω的活性位点与木瓜蛋白酶的活性位点无法区分。
