Cation control of chlorophyll a fluorescence yield in chloroplasts. Location of cation sensitive sites.
Cation control of chlorophyll a fluorescence yield in chloroplasts. Location of cation sensitive sites.
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DOI：
10.1016/0005-2728(76)90037-2
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发表时间：
1976-09
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影响因子：
--
通讯作者：
J. Mills;A. Telfer;J. Barber
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文献类型：
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作者：
J. Mills;A. Telfer;J. Barber
我们在几种不同的体外条件下比较了不同阳离子对叶绿体荧光产量的影响。1.在没有高能态但存在低浓度(10 MM)单价阳离子的情况下，二价金属阳离子以一种不涉及这些阳离子跨类囊体膜运输的方式增加了稳态叶绿素a的荧光产率。2.这种阳离子诱导的荧光上升动力学相对缓慢，似乎反映了阳离子结合(或随后的构象变化)到类囊体膜外表面的位置。3.在没有一价阳离子存在的情况下，镁离子与膜外侧位置的表观结合常数较低。加入低浓度的单价阳离子(10 MM)竞争性地抑制二价阳离子结合。4.荧光产量的控制也是通过高能态进行的，似乎涉及到类囊体内侧的质子/金属阳离子交换。5.分离的叶绿体在不含阳离子的介质中洗涤和再悬浮时，初始荧光水平较高，但在添加一价阳离子后被猝灭，EDTA钠比氯化钠有效得多。有人认为，当在这些条件下分离时，叶绿体保留了足够的二价阳离子来饱和外部负离子位点，而荧光降低是由于它们的去除。6.其他一些阳离子，如聚L-赖氨酸，可以不可逆地取代其外部位置的二价阳离子，导致固定的低荧光产率。
We have compared the effect of various cations on the fluorescence yield of chloroplasts under several different conditions in vitro. 1. In the absence of a high energy state but in the presence of low (10 mM) concentrations of monovalent cations, divalent metal cations increase steady state chlorophyll a fluorescence yield in a manner which does not involve transport of these cations across the thylakoid membranes. 2. The kinetics of this cation-induced fluorescence rise are relatively slow, and seem to reflect cation binding (or subsequent conformational changes) to sites on the outer surface of the thylakoid membrane. 3. In the absence of monovalent cations, the apparent binding constant for Mg2+ to sites on the outer side of the membrane is low. Addition of low concentrations of monovalent cations (10 mM) competitively inhibits divalent cation binding. 4. Control of fluorescence yield is also exerted by the high energy state, and seems to involve proton/metal cation exchange at sites on the inner side of the thylakoid. 5. When isolated chloroplasts are washed and resuspended in a medium containing no added cations, the initial fluorescence level is high, but is quenched on addition of monovalent cations, sodium EDTA being much more effective than sodium chloride. It is argued that when isolated under these conditions, chloroplasts retain sufficient divalent cations to saturate external negative sites, and that the fluorescence lowering is due to their removal. 6. Some other cations, such as poly (L-lysine), can displace divalent cations from their external sites in an irreversible manner, resulting in a fixed low fluorescence yield.