Institute für Biochemie der Pflanze, Universität Göttingen, Untere Karspüle 2, D-3400, Göttingen, Federal Republic of Germany.
Planta. 1988 Dec;174(4):534-41. doi: 10.1007/BF00634484.
The transport of glutamate, 2-oxoglutarate and malate in intact spinach chloroplasts was determined using a double-silicone-layer centrifugation technique in which the silicone layers stayed separated at the end of centrifugation. Glutamate was found to be transported via the dicarboxylate but not the 2-oxoglutarate translocator. Hence the kinetic parameters (i.e.K m,K i andV max) determined in glutamate-preloaded chloroplasts represent the kinetic constants of the dicarboxylate translocator. Measurements from malate- or succinate-preloaded chloroplasts represent the aggregate values of both the dicarboxylate and the 2-oxoglutarate translocators. Calculations showed that the 2-oxoglutarate and glutamate transport required to support the high fluxes of photorespiratory NH3 recycling could be achieved if the transport of these two dicarboxylates occurred on separate translocators. It is proposed that during photorespiration the transport of 2-oxoglutarate into and glutamate out of the chloroplast occurred via the 2-oxoglutarate and the dicarboxylate translocators, respectively. These transports are coupled to malate counter-exchange in a cascade-like manner resulting in a net 2-oxoglutarate/glutamate exchange with no net malate uptake.
使用双层硅脂层离心技术，在离心结束时硅脂层仍保持分离，测定完整菠菜叶绿体中谷氨酸、2-氧戊二酸和苹果酸的转运。发现谷氨酸通过二羧酸转运体而不是 2-氧戊二酸转运体进行转运。因此，在谷氨酸预加载叶绿体中确定的动力学参数（即 K m、K i 和 V max）代表二羧酸转运体的动力学常数。来自苹果酸或琥珀酸预加载叶绿体的测量值代表二羧酸和 2-氧戊二酸转运体的总和值。计算表明，如果这两种二羧酸的转运发生在单独的转运体上，则可以实现支持光呼吸 NH3 回收高通量所需的 2-氧戊二酸和谷氨酸转运。提出在光呼吸过程中，2-氧戊二酸通过 2-氧戊二酸转运体进入叶绿体，而谷氨酸通过二羧酸转运体从叶绿体输出。这些转运以级联方式与苹果酸反向交换偶联，导致 2-氧戊二酸/谷氨酸净交换，而无苹果酸净摄取。
