烟草核酮糖-1,5-二磷酸羧化酶/加氧酶四级结构的研究(英文)

本文提出三种证据证明烟草核酮糖-1,5-二磷酸羧化酶/加氧酶(Rubisco)的大亚基伸展在小亚基的外面,小亚基排列在大亚基中间的概念。证据是:1.固定化胰蛋白酶在一定条件下可水解RubisCO的大亚基但不水解小亚基,而天然胰蛋白酶水解大亚基,也水解小亚基。2.固定化抗小亚基IgG-Sepharose可与游离的小亚基相结合,但不能与全酶结合。3.低浓度尿素处理可使固定化的RubisCO-Sepharose上的小亚基解离下来,而大亚基仍结合在载体上,这说明RubisCO是通过定位在分子表面上的大亚基的ε-氨基与Sepharose共价偶联的。当RubisCO中的小亚基全部被解离后,大亚基之间的结合进一步增强,这时解离大亚基所需的尿素浓度要比小亚基存在时高。任何RubisCO的四级结构模型都应将小亚基置于大亚基中间受保护的位置,一部份小亚基可暴露于全酶分子表面。

Studies on the Quarternary Structure of Ribulose-1,5-bisphosphate Carboxylase/Oxygenase from Tobacco

Under controlled conditions immobilized trypsin can hydrolyze the large subunit, but not the samll subunit, while soluble trypsin hydrolyzes both the large and the small subunits. Isolated small subunit binds anti-small-subunit lgG-Sepharose, but the holoenzyme with its small subunit can not bind with the immobilized antibody. The small subunit is dissociated at low urea concentrations while the large subunit core is still bound to the matrix, which demonstrates that ribulose-1, 5-bispbosphate carboxylase/oxygenase is covalently coupled to Sepharose by virtue of the epsilon amino group of lysine on the large subunit. After complete dissociation of the small subunits, the hydrophobic attraction between large subunits is enhanced. The urea concentration required for dissociating the large subunit core is higher than when the small subunits are present. Any model of the quarternary structure of RubisCO should have the small subunit placed in a protected position among the large subunits with only limited area exposed to the outer surface of the holoenzyme.