Sukhareva B S, Tikhonenko A S, Dariĭ E L
Mol Biol (Mosk). 1994 Nov-Dec;28(6):1407-11.
It was shown by electron microscopy, that the native molecule of glutamate decarboxylase is a hexamer with dihedral symmetry; the subunits are situated at the apices of an octahedron. Apoenzyme at pH 6.0 is dissociated form. It were found s20.w - 12.8 +/- 0.54S and 5.51 +/- 0.43S for the native hexamer and a dissociated form, respectively. By column gel-filtration the molecular mass of the dissociated form was estimated as 105-106 kDa, this value corresponds to a dimer. There were 10 buried SH-groups per subunit in the hexamer, after dimer formation 8 of them became accessible. The reversible hexamer-dimer dissociation depends on pH and PLP. The pH dependences of the enzyme dissociation and activity are very similar. In the result of adding of 6 PLP equivalents to the dimers the reactivation and hexamer assembly were reached, the SH-groups burying preceded both these reactions. Effect of pH and PLP on the quaternary structure is known for some other PLP-enzymes. It may be the additional proof for the idea of a common ancestor for PLP-enzymes.
电子显微镜显示，谷氨酸脱羧酶的天然分子是具有二面体对称性的六聚体；亚基位于八面体的顶点。pH 6.0时的脱辅酶呈解离形式。天然六聚体和解离形式的沉降系数分别为s20.w - 12.8 +/- 0.54S和5.51 +/- 0.43S。通过柱凝胶过滤，解离形式的分子量估计为105 - 106 kDa，该值对应于二聚体。六聚体中每个亚基有10个埋藏的SH基团，形成二聚体后其中8个变得可及。六聚体 - 二聚体的可逆解离取决于pH和磷酸吡哆醛（PLP）。酶解离和活性的pH依赖性非常相似。向二聚体中加入6当量的PLP后，实现了再活化和六聚体组装，SH基团的埋藏先于这两个反应。pH和PLP对四级结构的影响在其他一些PLP酶中也有报道。这可能是PLP酶有共同祖先这一观点的额外证据。
