Department of Agronomy, University of Wisconsin, Madison, Wisconsin 53706.
Plant Physiol. 1985 Sep;79(1):242-7. doi: 10.1104/pp.79.1.242.
Pyruvate decarboxylase (PDC) was purified from mature, dry maize kernels and from roots of anaerobically treated maize seedlings and partially characterized. PDC was purified to a specific activity of 96 units per milligram protein from kernels and to 41 units per milligram protein from root. The subunit molecular masses were estimated to be 61,000 and 60,000 for kernel PDC and 59,000 and 58,000 for root PDC. The pH optimum for each enzyme was 5.8. Since the pH optimum is nearly one pH unit below the value reported for the cytoplasm of anaerobically metabolizing maize roots (pH 6.7 +/- 0.2), we investigated the effects of pH 5.8 and 6.6 on the cooperative kinetics observed for PDC from each source. The maximum Hill coefficients (n(H)) were much greater at each pH for the kernel PDC (pH 5.8, n(H) = 2.5 and pH 6.6, n(H) = 3.2) than for the root PDC (pH 5.8, n(H) = 1.4 and pH 6.6, n(H) = 1.8). The cooperative kinetics observed with respect to pyruvate were asymmetric. Potassium inhibited maize PDC and was competitive with pyruvate (root PDC K(i) = 16 millimolar and kernel PDC K(i) = 10 millimolar).
丙酮酸脱羧酶（PDC）从成熟干燥的玉米粒和厌氧处理的玉米幼苗的根部中被分离出来并进行了部分特性描述。PDC 从玉米粒中被提纯至每毫克蛋白 96 个单位的比活度，从根部中被提纯至每毫克蛋白 41 个单位的比活度。亚基的分子量估计为 61000 和 60000，分别用于核 PDC 和根 PDC。每种酶的最适 pH 为 5.8。由于最适 pH 值比报道的厌氧代谢玉米根细胞质的 pH 值低近 1 个单位（pH 6.7 +/- 0.2），我们研究了 pH 值为 5.8 和 6.6 对来自每个来源的 PDC 观察到的协同动力学的影响。在每个 pH 值下，核 PDC 的最大 Hill 系数（n(H)）（pH 5.8，n(H) = 2.5 和 pH 6.6，n(H) = 3.2）都远大于根 PDC（pH 5.8，n(H) = 1.4 和 pH 6.6，n(H) = 1.8）。对于丙酮酸观察到的协同动力学是不对称的。钾抑制玉米 PDC，与丙酮酸竞争（根 PDC K(i) = 16 毫摩尔和核 PDC K(i) = 10 毫摩尔）。
