摘要
Aim Cysteine proteases are closely associated with many human and non-human pathological processes and are potential targets for metal ions especially Hg^2＋ and the related species. In the present work, on the basis of to the general study on the effects of some metal ions on the activity of papain, a well-known representative of cysteine protease family, the inhibitory effects of Hg^2＋ and polysulfide complexes were studied. Results All the metal ions tested （Hg^2＋, Cu^2＋, Ag^＋, Au^3＋, Zn^2＋, Cd^2＋, Fe^3＋, Mn^2＋, Pb^2＋, Yb^3＋） inhibit the activity of papain anda good correlation between the inhibitory potency and softness-and-hardness was observed. Among the metals, Hg^2＋ was shown to be a potent inhibitor of papain with a Kiof 2 × 10^-7 mol·L^-1 among. Excessive amounts of glutathione and cysteine could reactivate the enzyme activity of papain deactivated by Hg^2＋. These evidences supported that Hg^2＋ might bind to the catalytic site of papain. Interestingly, Hg （Ⅱ） polysulfide complexes were for the first time found to inhibit papain with a Ki of 7 × 10^-6 mol·L^-1, whose potency is close to a well known mercury compound, thimerosal （Ki=2.7 × 10^-6）. In addition, Hg （Ⅱ） polysulfide complexes exhibit good permeability （ 1.9 × 10-5 cm· s^-1） to caco-2 monolayer. Conclusion These results suggested that mercury polysulfide complexes might be potential bioactive species in the interaction with cysteine proteases and other- SH-content proteins, providing a new clue to understand the mechanism of the toxicological and pharmacological actions of cinnabar and other insoluble mercury compounds.
目的半胱氨酸蛋白酶参与了很多动植物生理过程和病理过程,是Hg2+及其化合物作用的潜在靶点。木瓜蛋白酶是半胱氨酸蛋白酶家族中最具代表性、研究最为广泛深入的一种蛋白酶,本文以木瓜蛋白酶为模型, 研究了汞等金属离子及其化合物对半胱氨酸蛋白酶活性的抑制作用。结果 Hg2+对木瓜蛋白酶活性的抑制能力很强(Ki=2×10-7 mol·L-1)。过量的还原型谷胱甘肽和半胱氨酸能够恢复木瓜蛋白酶的活性。多种金属离子(Cu2+、Ag+、Au3+、Zn2+、Cd2+、Fe3+、Mn2+、Pb2+、Yb3+)对木瓜蛋白酶的活性具有抑制能力,而且抑制能力与金属离子自身的软硬度具有良好的相关性。研究结果表明 Hg2+ 可能作用于木瓜蛋白酶的活性中心。此外,本文首次研究了汞多硫化物复合物对木瓜蛋白酶活性的抑制作用,发现其表观抑制常数(Ki= 7×10-6 mol·L-1)与柳硫汞(Ki=2.7×10-6mol·L-1)十分接近,而且其caco-2细胞单层的表观渗透能力(1.9×10-5cm/s) 也较好。结论汞多硫化物复合物可能通过与半胱氨酸蛋白酶或者其它含巯基蛋白分子作用,发挥生物学活性。本文的研究工作可能有助于阐明汞化合物( 特别是朱砂等不溶性汞化合物) 的毒理及药理作用的机制。
