Brown G K, Fox R M, O'Sullivan W J
J Biol Chem. 1975 Sep 25;250(18):7352-8.
Orotidylate decarboxylase has been purified approximately 300-fold from human erythrocytes. It was shown to exist in three molecular weight forms, a probable monomer of molecular weight 62,000, a dimer, and a tetramer. Conversion of the monomer to higher molecular weight forms was associated with increased stability to thermal inactivation and was promoted by a number of low molecular weight compounds, including orotic acid and competitive inhibitors of the enzyme. Orotic acid phosphoribosyltransferase co-purified with the decarboxylase but was much more susceptible to inactivation. The partially purified orotidylate decarboxylase showed a triphasic Lineweaver-Burk plot when examined over a wide range of substrate concentrations. The separated molecular weight forms gave linear double reciprocal plots with Km values corresponding to the three values obtained with the erythrocyte enzyme preparation. The values obtained were 25, 3, and 0.6 muM for the monomer, dimer, and tetramer forms, respectively.
乳清酸脱羧酶已从人红细胞中纯化了约300倍。它以三种分子量形式存在，一种可能的分子量为62,000的单体、一种二聚体和一种四聚体。单体向更高分子量形式的转变与对热失活的稳定性增加有关，并受到多种低分子量化合物的促进，包括乳清酸和该酶的竞争性抑制剂。乳清酸磷酸核糖基转移酶与脱羧酶共纯化，但对失活更敏感。在很宽的底物浓度范围内检测时，部分纯化的乳清酸脱羧酶呈现三相Lineweaver-Burk图。分离出的分子量形式给出线性双倒数图，其Km值对应于用红细胞酶制剂获得的三个值。单体、二聚体和四聚体形式分别得到的值为25、3和0.6 μM。
