Shimada K, Berg H C
J Mol Biol. 1987 Feb 5;193(3):585-9. doi: 10.1016/0022-2836(87)90269-5.
Cells of a motile Streptococcus were starved, tethered to a quartz coverslip, energized with a potassium diffusion potential, and exposed to sudden decrements in external pH generated by flash photolysis of 2-hydroxyphenyl-1-(2-nitro)phenyl phosphate. The rotation rate of the cells increased following the flash but only after a brief time lag. Lags of the order of 0.1 second were observed in a dilute buffer (0.05 mM), confirming results obtained earlier. These lags were longer when the buffer was prepared in D2O. However, lags as short as 0.01 second were found in more concentrated buffers (1 and 3 mM). In this case, there was no deuterium solvent isotope effect. These differences arise from the extra time required for diffusion of protons from a dilute medium into the cell wall, which has a large buffering capacity. The short lags observed in concentrated media could be inherent to the flagellar motor, but the possibility that they are due to buffered diffusion through the cell wall or to elastic filtering by the tether has not been ruled out.
将运动性链球菌细胞饥饿处理后，固定在石英盖玻片上，利用钾离子扩散电位供能，并通过对2-羟基苯基-1-（2-硝基）苯基磷酸进行闪光光解产生外部pH值的突然降低，使其暴露于这种环境中。闪光后细胞的旋转速率增加，但有短暂的时间延迟。在稀缓冲液（0.05 mM）中观察到约0.1秒的延迟，证实了早期获得的结果。当缓冲液用重水配制时，这些延迟会更长。然而，在浓度更高的缓冲液（1和3 mM）中发现延迟短至0.01秒。在这种情况下，不存在氘溶剂同位素效应。这些差异源于质子从稀介质扩散到具有大缓冲能力的细胞壁所需的额外时间。在浓缩介质中观察到的短延迟可能是鞭毛马达固有的，但它们是由于通过细胞壁的缓冲扩散或系链的弹性过滤所致的可能性尚未排除。
