Adair W S, Wolfe J
J Cell Physiol. 1977 Jul;92(1):77-90. doi: 10.1002/jcp.1040920110.
The rate of uridine uptake in Tetrahymena declines by an order of magnitude by two hours after shiftdown to a non-nutrient buffer. This alteration in uptake properties cannot be accounted for by an increase in the intracellular pool of uridine, an increase in apparent Km for uptake or a decline in the rate in which uridine is processed intracellularly. It is argued that the decrease in uridine uptake is due to a reduction in numbers of functional transport molecules exposed at the cell surface and is a reflection of a developmentally related cell surface transformation. In addition, the putative decline in functional transport molecules cannot be entirely explained by metabolic turnover of these molecules in the absence of replacement, nor does it require the synthesis of new protein. We discuss the possibility that a shift in equilibrium between accessible and inaccessible transporters is operating. Finally, a close correlation between conditions which elicit the transport alteration and those which allow the development of mating competency suggests that the two phenomena may be coordinately regulated.
在转移到无营养缓冲液两小时后，四膜虫中尿苷摄取速率下降了一个数量级。摄取特性的这种改变不能用细胞内尿苷池的增加、摄取的表观 Km 的增加或尿苷在细胞内加工速率的下降来解释。有人认为，尿苷摄取的减少是由于细胞表面暴露的功能性转运分子数量减少，这是与发育相关的细胞表面转变的一种反映。此外，功能性转运分子假定的减少不能完全用这些分子在没有替换的情况下的代谢周转来解释，也不需要合成新的蛋白质。我们讨论了可及和不可及转运体之间平衡发生变化的可能性。最后，引发转运改变的条件与允许交配能力发展的条件之间的密切相关性表明，这两种现象可能受到协同调节。
