Department of Botany, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Plant Physiol. 1983 Aug;72(4):1062-7. doi: 10.1104/pp.72.4.1062.
Intact plastids from greening maize (Zea mays L.) leaves converted [(14)C]glutamate and [(14)C]2-ketoglutarate (KG) to [(14)C]5-aminolevulinic acid (ALA). Glutamate appeared to be the immediate precursor of ALA, while KG was first converted to glutamate, as shown by the effect of various inhibitors of amino acid metabolism. Plastids from greening leaves contained markedly higher activity as compared with etioplasts or chloroplasts. The synthesis of ALA by intact plastids was light dependent. The enzyme system resides in the stroma of plastids or may be lightly bound to membranes. The solubilized system showed maximal activity around pH 7.9 and required Mg(2+), ATP, and NADPH although dependence on the latter was not clear-cut. A relatively high level of activity could be extracted from etioplasts. Maximal activity was obtained from plastids of leaves which had been illuminated for 90 minutes, after which activity declined sharply. The enzyme system solubilized from plastids also catalyzed the conversion of putative glutamate 1-semialdehyde to ALA in a reaction which was not dependent on the addition of an amino donor.The system in maize greatly resembled the one which had been reported from barley. It is suggested that this system is the one responsible for the biosynthesis of ALA destined for chlorophyll formation.
完整的质体从绿化的玉米（玉米）叶片中将[(14)C]谷氨酸和[(14)C]2-酮戊二酸（KG）转化为[(14)C]5-氨基酮戊酸（ALA）。谷氨酸似乎是 ALA 的直接前体，而 KG 首先转化为谷氨酸，这可以通过各种氨基酸代谢抑制剂的作用来证明。与黄化质体或叶绿体相比，绿化叶片中的质体具有明显更高的活性。完整质体合成 ALA 是光依赖性的。该酶系统位于质体的基质中，或者可能与膜轻微结合。溶解系统在 pH 值 7.9 左右显示出最大活性，并且需要 Mg(2+)、ATP 和 NADPH，但对后者的依赖性并不明显。可以从黄化质体中提取出相对较高水平的活性。最大活性是从已经照射 90 分钟的叶片的质体中获得的，之后活性急剧下降。从质体中溶解的酶系统还可以催化假定的谷氨酸 1-半醛向 ALA 的转化，该反应不依赖于氨基酸供体的添加。该系统在玉米中非常类似于已经从大麦中报道的系统。建议该系统是负责用于叶绿素形成的 ALA 生物合成的系统。
