Bryant J, Green T R, Gurusaddaiah T, Ryan C A
Biochemistry. 1976 Aug 10;15(16):3418-24. doi: 10.1021/bi00661a004.
Proteinase inhibitor II, an inhibitor of chymotrypsin and trypsin, is a heat-stable protein with a dimeric molecular weight of 21 000 that is a component of Russet Burbank potato tubers. Four monomeric isoinhibitor species of molecular weight 10 500 comprise inhibitor II and were isolated by chromatography on phosphocellulose in 8 M urea. Upon removal of the urea, each monomeric species dimerized to yield homogeneous dimers. The three major protomer species, called B, C, and D, and their homogeneous dimers were further characterized. They have similar molecular weights and amino acid compositions, and each has an N-terminal alanine residue. Dimers of purified protomers B, C, and D exhibited full cross-reactivities with each other in immunological double-diffusion assays. Reconstituted dimers possess two binding sites for bovine alpha-chymotrypsin, indicating that each monomer possesses one binding site for this enzyme. Significant differences were noted among the reconstituted dimers in their isoelectric points, immunoelectrophoretic mobilities, ion-exchange properties, and their inhibitory reactivities against trypsin. The properties of the inhibitor II dimeric species are similar but not identical to inhibitors IIa and IIb reported from Japanese potatoes (variety "Danshaku-Imo"), indicating the existence of intervarietal, as well as intravarietal, differences among potato tuber inhibitor II isoinhibitors.
蛋白酶抑制剂II是一种胰凝乳蛋白酶和胰蛋白酶的抑制剂，是一种热稳定蛋白，分子量为21000，呈二聚体形式，是褐皮伯班克马铃薯块茎的组成成分。分子量为10500的四种单体同工抑制剂构成了抑制剂II，并通过在8M尿素中于磷酸纤维素上进行色谱分离而得到。去除尿素后，每种单体形式二聚化形成均一的二聚体。对三种主要的原体形式，即B、C和D，以及它们的均一二聚体进行了进一步表征。它们具有相似的分子量和氨基酸组成，且每种都有一个N端丙氨酸残基。纯化的原体B、C和D的二聚体在免疫双扩散试验中彼此表现出完全的交叉反应性。重构的二聚体对牛α-胰凝乳蛋白酶有两个结合位点，表明每个单体对该酶有一个结合位点。在重构的二聚体的等电点、免疫电泳迁移率、离子交换特性以及它们对胰蛋白酶的抑制反应性方面发现了显著差异。抑制剂II二聚体形式的特性与从日本马铃薯（品种“丹作芋”）报道的抑制剂IIa和IIb相似但不相同，这表明马铃薯块茎抑制剂II同工抑制剂之间存在品种间以及品种内的差异。
