Jamieson J D, Palade G E
J Cell Biol. 1971 Mar;48(3):503-22. doi: 10.1083/jcb.48.3.503.
We have examined, in the pancreatic exocrine cell, the metabolic requirements for the conversion of condensing vacuoles into zymogen granules and for the discharge of the contents of zymogen granules. To study condensing vacuole conversion, we pulse labeled guinea pig pancreatic slices for 4 min with leucine-(3)H and incubated them in chase medium for 20 min to allow labeled proteins to reach condensing vacuoles. Glycolytic and respiratory inhibitors were then added and incubation continued for 60 min to enable labeled proteins to reach granules in control slices. Electron microscope radioautography of cells or of zymogen granule pellets from treated slices showed that a large proportion of prelabeled condensing vacuoles underwent conversion in the presence of the combined inhibitors. Osmotic fragility studies on zymogen granule suspensions suggest that condensation may result from the aggregation of secretory proteins in an osmotically inactive form. Discharge was studied using an in vitro radioassay based on the finding that prelabeled zymogen granules can be induced to release their labeled contents to the incubation medium by carbamylcholine or pancreozymin. Induced discharge is not affected if protein synthesis is blocked by cycloheximide for up to 2 hr, but is strictly dependent on respiration. The data indicate that transport and discharge do not require the pari passu synthesis of secretory or nonsecretory proteins (e.g. membrane proteins), suggesting that the cell may reutilize its membranes during the secretory process. The energy requirements for zymogen discharge may be related to the fusion-fission of the granule membrane with the apical plasmalemma.
我们研究了胰腺外分泌细胞中，浓缩泡转化为酶原颗粒以及酶原颗粒内容物排出的代谢需求。为了研究浓缩泡的转化，我们用亮氨酸 -（3）H对豚鼠胰腺切片进行4分钟的脉冲标记，然后在追踪培养基中孵育20分钟，以使标记的蛋白质到达浓缩泡。接着加入糖酵解和呼吸抑制剂，并继续孵育60分钟，以使标记的蛋白质在对照切片中到达颗粒。对处理过的切片的细胞或酶原颗粒沉淀进行电子显微镜放射自显影显示，在联合抑制剂存在的情况下，很大一部分预先标记的浓缩泡发生了转化。对酶原颗粒悬浮液的渗透脆性研究表明，浓缩可能是由于分泌蛋白以渗透惰性形式聚集所致。利用基于以下发现的体外放射测定法研究排出：预先标记的酶原颗粒可被氨甲酰胆碱或促胰液素诱导将其标记的内容物释放到孵育培养基中。如果用环己酰亚胺阻断蛋白质合成长达2小时，诱导的排出不受影响，但严格依赖于呼吸作用。数据表明，运输和排出不需要同时合成分泌性或非分泌性蛋白质（如膜蛋白），这表明细胞在分泌过程中可能会重新利用其膜。酶原排出的能量需求可能与颗粒膜与顶端质膜的融合 - 裂变有关。
