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首页> 外文期刊>Journal of bacteriology >Steady-State Measurement of the Turnover of Amino Acid in the Cellular Proteins of Growing Escherichia coli: Existence of Two Kinetically Distinct Reactions
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Steady-State Measurement of the Turnover of Amino Acid in the Cellular Proteins of Growing Escherichia coli: Existence of Two Kinetically Distinct Reactions

机译：稳态细胞生长的大肠杆菌细胞蛋白中氨基酸转换的量度：两个动力学不同反应的存在。

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Turnover of cellular protein has been estimated in Escherichia coli during continuous exponential growth and in the absence of extensive experimental manipulation. Estimation is based upon the cumulative release into carrier pools of free leucine-1-14C over a number of time intervals after its pulsed incorporation into protein. Breakdown rates obtained with other labeled amino acids are similar to those obtained with leucine. Two kinetically separate processes have been shown. First, a very rapid turnover of 5% of the amino acid label occurs within 45 sec after its incorporation, most likely indicating maturative cleavages within the proteins after their assembly. A slower heterogeneous rate of true protein turnover follows, falling by 39% in the remaining proteins for each doubling of turnover time. At 36 C, the total breakdown rate of cellular protein is 2.5 and 3.0% per hr over a threefold range of growth rate in glucose and acetate medium, respectively. This relatively constant breakdown rate is maintained during slower growth by more extensive protein replacement, one fifth of the protein synthesized at any time in the acetate medium being replaced after 4.6 doubling times. Intracellular proteolysis thus appears to be a normal and integral reaction of the growing cell. The total rate equals minimal estimates obtained by others for arrested or decelerated growth but is kinetically more heterogeneous. Quantitatively proteolysis is not directly affected by growth arrestment per se as caused by α-methylhistidine, chloramphenicol, or uncouplers of oxidative phosphorylation, but qualitatively it can gradually become more homogeneous kinetically as a secondary event of starvation. Under more extreme conditions as with extensive washing, prolonged phosphorylative uncoupling, or acidification of the growth medium, the proteolytic rate can increase severalfold.
机译：在连续的指数生长过程中和没有广泛实验操作的情况下，估计大肠杆菌中细胞蛋白的周转率。估计是基于在脉冲掺入游离亮氨酸- 1 - 14 C 后一段时间内向载体库的累积释放蛋白。用其他标记氨基酸获得的分解率与用亮氨酸获得的分解率相似。已经显示了两个动力学上分开的过程。首先，氨基酸标记掺入后的45秒内会发生5％的非常快速的周转，很可能表明蛋白质在组装后会发生成熟性切割。随之而来的是真正的蛋白质转换的异质速度变慢，转换时间每增加一倍，剩余蛋白质中的异质速度就会下降39％。在36℃下，在葡萄糖和乙酸盐培养基中的三倍生长速率范围内，细胞蛋白的总分解速率分别为每小时2.5％和3.0％。在较慢的生长过程中，可以通过更广泛的蛋白质替换来维持这种相对恒定的分解速率，在4.6倍的倍增时间之后，醋酸盐培养基中随时合成的蛋白质的五分之一会被替换。因此，细胞内蛋白水解似乎是生长中细胞的正常反应。总速率等于其他人对于停滞或减速生长所获得的最小估计值，但在动力学上更加不均一。定量蛋白水解本身不受α-甲基组氨酸，氯霉素或氧化磷酸化解偶联剂引起的生长停滞本身的直接影响，但从质上说，它可以在动力学上逐渐变得更加均匀，这是饥饿的第二个事件。在更极端的条件下，例如广泛洗涤，长时间磷酸化解偶联或生长培养基酸化的情况下，蛋白水解速率可能会增加几倍。

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