Lloyd J B
Ciba Found Symp. 1979(75):151-65. doi: 10.1002/9780470720585.ch10.
Pinocytosis is a widespread phenomenon and involves the internalization of large amounts of plasma membrane. Much of this membrane is probably returned to the plasma membrane in vesicular form, and reasons are advanced why this recycling may occur chiefly before pinosome--lysosome fusion and may be related to vacuole fusion events. Some internalized membrane must nevertheless enter the lysosomal compartment and, in order to maintain a steady state, must be removed at the same rates as it enters. This constant lysosomal involution probably occurs by the budding of vesicles either inward (for digestion) or outward (for return to the plasma membrane). The former process allows for the transfer of cytosol components into the lysosome. Quantitative studies on pinocytosis have shown that selective substrate capture is commonly achieved by the adsorption of substances to the plasma membrane being internalized. In contrast the basal rate of uptake of liquid and membrane is not easily modified. If similar considerations apply to uptake by the quasi-pinocytic lysosomal involution, modification of proteins leading to adsorption to the cytoplasmic face of the lysosome could be the rate-determining step in the degradation of endogenous cytoplasmic proteins by lysosomes.
胞饮作用是一种广泛存在的现象,涉及大量质膜的内化。其中许多膜可能以囊泡形式返回质膜,文中提出了这种循环可能主要发生在胞饮体 - 溶酶体融合之前的原因,并且可能与液泡融合事件有关。然而,一些内化的膜必须进入溶酶体区室,为了维持稳态,必须以与进入相同的速率被清除。这种持续的溶酶体内卷可能通过向内(用于消化)或向外(用于返回质膜)出芽形成囊泡来发生。前一过程允许胞质溶胶成分转移到溶酶体中。对胞饮作用的定量研究表明,选择性底物捕获通常是通过物质吸附到正在内化的质膜上来实现的。相比之下,液体和膜的基础摄取速率不易改变。如果类似的考虑适用于准胞饮性溶酶体内卷的摄取,那么导致蛋白质吸附到溶酶体胞质面的修饰可能是溶酶体降解内源性胞质蛋白的限速步骤。