Department of Biology, University of California, Riverside, California 92502.
Plant Physiol. 1973 Mar;51(3):439-47. doi: 10.1104/pp.51.3.439.
A detailed comparison of green leaf phosphoenolpyruvate carboxylases from the C(4)-species Atriplex spongiosa and the C(3)-species Atriplex hastata revealed significant physical and kinetic differences. The two alloenzymes can be separated by anion exchange chromatography but have comparable molecular weights (350,000). Maximal velocity estimates were 38.0 and 1.48 micromoles per minute per milligram of chlorophyll for the carboxylases of A. spongiosa and A. hastata, respectively. Km phosphoenolpyruvate estimates were 0.49 and 0.08 mm for the C(4)A. spongiosa and C(3)A. hastata and the Km Mg estimates were 0.33 mm for the C(4) species and 0.017 mm for the C(3) species. The activity of the phosphoenolpyruvate carboxylase of A. spongiosa is more sensitive to chloride and phosphate than the phosphoenolpyruvate carboxylase of A. hastata, but both are equally sensitive to Mg chelating substances such as ATP, ADP, and citrate if assayed at their respective Km Mg values. A survey of the phosphoenolpyruvate carboxylases from 18 C(4) and C(3) species resulted in mean maximal velocity estimates of 29.0 +/- 13.2 and 1.50 +/- 0.57 micromoles per minute per milligram of chlorophyll for the C(4) species and C(3) species, respectively. Km phosphoenolpyruvate estimates were 0.59 +/- 0.35 mm and 0.14 +/- 0.07 mm for the C(4) and C(3), and Km Mg estimates were 0.50 +/- 0.30 and 0.097 +/- 0.057 mm for C(4) and C(3). All differences between means were significant at the 0.01 confidence level, supporting our hypothesis that the phosphoenolpyruvate carboxylase alloenzymes of C(4) and C(3) plants are functionally different and are associated with different photosynthetic roles. Both function in the photosynthetic production of C(4) acids, the phosphoenolpyruvate carboxylase of C(4) species largely producing malate or aspartate (or both) as a photosynthetic intermediate and the phosphoenolpyruvate carboxylase of C(3) species producing malate or aspartate (or both) as a photosynthetic product.
对来自 C(4)物种 Atriplex spongiosa 和 C(3)物种 Atriplex hastata 的绿叶磷酸烯醇丙酮酸羧化酶的详细比较表明，它们在物理性质和动力学方面存在显著差异。这两种同工酶可以通过阴离子交换色谱分离，但分子量相当（350,000）。羧化酶的最大速度估计值分别为每分钟每毫克叶绿素 38.0 和 1.48 微摩尔，对于 A. spongiosa 和 A. hastata 的羧化酶。Km 磷酸烯醇丙酮酸的估计值分别为 0.49 和 0.08 mM，对于 C(4)A. spongiosa 和 C(3)A. hastata，Km Mg 的估计值分别为 0.33 mM，对于 C(4)物种和 0.017 mM，对于 C(3)物种。A. spongiosa 磷酸烯醇丙酮酸羧化酶的活性对氯离子和磷酸盐比 A. hastata 的磷酸烯醇丙酮酸羧化酶更敏感，但如果在各自的 Km Mg 值下进行测定，两者对 Mg 螯合物质（如 ATP、ADP 和柠檬酸）同样敏感。对 18 种 C(4)和 C(3)物种的磷酸烯醇丙酮酸羧化酶的调查得出，C(4)物种和 C(3)物种的最大速度估计值分别为每分钟每毫克叶绿素 29.0 +/- 13.2 和 1.50 +/- 0.57 微摩尔。Km 磷酸烯醇丙酮酸的估计值分别为 0.59 +/- 0.35 mM 和 0.14 +/- 0.07 mM，Km Mg 的估计值分别为 0.50 +/- 0.30 mM 和 0.097 +/- 0.057 mM，用于 C(4)和 C(3)。均值之间的所有差异均在 0.01 置信水平上具有统计学意义，支持我们的假设，即 C(4)和 C(3)植物的磷酸烯醇丙酮酸羧化酶同工酶在功能上不同，与不同的光合作用角色相关。两者都在 C(4)酸的光合作用生产中起作用，C(4)物种的磷酸烯醇丙酮酸羧化酶主要产生苹果酸或天冬氨酸（或两者）作为光合作用中间体，而 C(3)物种的磷酸烯醇丙酮酸羧化酶产生苹果酸或天冬氨酸（或两者）作为光合作用产物。
