Department of Plant Science, University of Delaware, Newark, Delaware 19711.
Plant Physiol. 1982 Sep;70(3):723-7. doi: 10.1104/pp.70.3.723.
Kinetics of two molecular forms of K-dependent citrate dehydrase in maize (Zea mays L.) are reported. The isozymes, designated CD I and CD II, were found to be compartmented in mitochondria and cytosol, respectively.CD I exhibited hyperbolic kinetics with respect to both citrate and potassium with K(m) 2.3 and 12 millimolar, respectively. Maximum velocity was 0.38 micromole of trans-aconitic acid per minute per milligram protein. The pH optimum was 7.2. trans-aconitic synthesis by CD I is regulated by both citrate concentration and pH.CD II exhibited hyperbolic kinetics with respect to citrate (K(m) 0.6 millimolar) but sigmoidal kinetics with respect to potassium. trans-aconitic acid synthesis by CD II is regulated by potassium. This may account for the positive correlation between leaf potassium and trans-aconitic acid in certain grasses (Clark 1968 Crop Sci 8: 165).
两种玉米(Zea mays L.)依赖于 K 的柠檬酸脱水酶的分子形式的动力学被报道。同工酶,分别命名为 CD I 和 CD II,被发现在线粒体和细胞质中分别存在。CD I 对柠檬酸和钾都表现出双曲线动力学,K(m) 分别为 2.3 和 12 毫摩尔。最大速度为每分钟每毫克蛋白 0.38 微摩尔反丁烯二酸。最适 pH 为 7.2。CD I 对柠檬酸的合成受柠檬酸浓度和 pH 的调节。CD II 对柠檬酸(K(m) 0.6 毫摩尔)表现出双曲线动力学,但对钾表现出 S 形动力学。CD II 对反丁烯二酸的合成受钾的调节。这可以解释在某些禾本科植物中叶片钾和反丁烯二酸之间的正相关关系(Clark 1968 Crop Sci 8: 165)。