Lomax T L, Mehlhorn R J
Biochim Biophys Acta. 1985 Nov 21;821(1):106-14. doi: 10.1016/0005-2736(85)90160-9.
Volumes and pH gradients were determined with spin probes in liposomes and zucchini membrane vesicles by quantitating the internal concentrations of probes in the presence of an impermeable line-broadening agent, manganese + EDTA. Volume shrinkage in response to increasing external concentrations of MnEDTA was consistent with perfect osmotic behavior of both vesicle populations. Buffer additions were used to impose pH gradients on the vesicles; liposome gradients measured with a spin-labeled weak acid were slightly smaller than the maximum theoretical imposed gradients, whereas above a threshold magnitude, measured gradients for the plant membranes were significantly smaller than imposed gradients. However, the residual pH gradient in the zucchini vesicles decreased at about the same rate as the liposome gradient. Moreover, this residual gradient was not completely collapsed in the presence of the proton ionophore, FCCP, indicating that the vesicles were impermeable to ions; indeed, ion permeabilities of both vesicle preparations appeared to be similar during the slow phase of the pH gradient collapse. Thus, zucchini membrane vesicles are tightly sealed and appear to have a mechanism for dissipating pH gradients rapidly when these gradients exceed some threshold value.
通过在不可渗透的线宽展剂锰离子 + 乙二胺四乙酸（MnEDTA）存在的情况下定量探针的内部浓度，使用自旋探针测定脂质体和西葫芦膜囊泡中的体积和pH梯度。响应于外部MnEDTA浓度增加的体积收缩与两种囊泡群体的完美渗透行为一致。添加缓冲液以在囊泡上施加pH梯度；用自旋标记的弱酸测量的脂质体梯度略小于最大理论施加梯度，而高于阈值幅度时，植物膜的测量梯度明显小于施加梯度。然而，西葫芦囊泡中的残余pH梯度以与脂质体梯度大致相同的速率下降。此外，在质子离子载体羰基氰化物间氯苯腙（FCCP）存在的情况下，这种残余梯度并未完全消失，表明囊泡对离子不可渗透；实际上，在pH梯度崩溃的缓慢阶段，两种囊泡制剂的离子渗透率似乎相似。因此，西葫芦膜囊泡密封紧密，并且当这些梯度超过某个阈值时，似乎具有快速消散pH梯度的机制。
