ADP-Glucose Pyrophosphorylase Is Located in the Plastid in Developing Tomato Fruit

The subcellular location of activity and protein of ADP-glucose pyrophosphorylase (AGPase) in developing tomato (Lycopersicon esculentum) fruit was determined following a report that the enzyme might be present inside and outside the plastids in this organ. Plastids prepared from crude homogenates of columella and pericarp, the starch-accumulating tissues of developing fruit, contained 8% to 18% of the total activity of enzymes known to be confined to plastids, and 0.2% to 0.5% of the total activity of enzymes known to be confined to the cytosol. The proportion of the total activity of AGPase in the plastids was the same as that of the enzymes known to be confined to the plastid. When samples of plastid and total homogenate fractions were subjected to immunoblotting with an antiserum raised to AGPase, most or all of the protein detected was plastidial. Taken as a whole, these data provide strong evidence that AGPase is confined to the plastids in developing tomato fruit.

本研究基于此前一则关于ADP葡萄糖焦磷酸化酶（ADP-glucose pyrophosphorylase，AGPase）可能在番茄（Lycopersicon esculentum）果实的质体内外均有分布的报道，对发育中番茄果实内该酶的酶活性与蛋白的亚细胞定位进行了测定。从发育中番茄果实的淀粉积累组织——果髓（columella）和果皮（pericarp）的粗匀浆中分离得到的质体，其所含酶活性占已知仅定位于质体的酶总活性的8%~18%，占已知仅定位于胞质溶胶（cytosol）的酶总活性的0.2%~0.5%。ADP葡萄糖焦磷酸化酶在质体中的总活性占比，与已知仅定位于质体的酶的活性占比一致。当用针对该酶制备的抗血清对质体组分及总匀浆组分的样品进行免疫印迹（immunoblotting）分析时，检测到的蛋白绝大部分或全部均为质体定位型。综合上述所有数据，本研究为发育中的番茄果实内ADP葡萄糖焦磷酸化酶仅定位于质体这一结论提供了强有力的实验证据。