PH-DISSOCIATION CHARACTERISTICS OF CARDIOLIPIN AND ITS 2'-DEOXY ANALOG
PH-DISSOCIATION CHARACTERISTICS OF CARDIOLIPIN AND ITS 2'-DEOXY ANALOG
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DOI：
10.1007/bf02537494
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发表时间：
1993-10-01
期刊：
影响因子：
1.9
通讯作者：
HAINES, TH
中科院分区：
文献类型：
--
作者：
KATES, M;SYZ, JY;HAINES, TH
心磷脂(CL)存在于有氧原核生物的线粒体膜和质膜中。CL与氧化磷酸化相关的跨膜酶紧密结合。早些时候有报道称，CL在低pH值下只有一个PK。我们在水悬浮液(双层)和甲醇/水(1：1，体积/体积)溶液中滴定CL，发现它有两个不同的pK值，pK1为2.8，pK2为7.5，但随着滴定过程的进行，pK2向上移动到9.5。异常高的pK2可能是由于形成了一个独特的氢键，其中中心甘油上的游离羟基与一个质子化的磷酸(P-OH基团)形成了环状的分子内氢键结构。因此，我们用化学方法合成了缺少中心羟基的2‘-脱氧心磷脂类似物，并在与CL相同的条件下，用电位滴定法测定了它的pH离解行为。羟基的缺失极大地改变了滴定过程，使脱氧类似物呈现出两个紧密间隔的低pK值(pK1=1.8；pK2=4.0)。CL第二离解常数的异常滴定行为可能归因于中心甘油羟基参与了环状氢键单质子化CL的形成，在较高的pH条件下，它可能是质子的储存库。这一功能可能对生物膜中的质子泵有重要影响。
Cardiolipin (CL) is found in inner mitochondrial membranes and the plasma membrane of aerobic prokaryotes. CL is tightly bound to those transmembrane enzymes associated with oxidative phosphorylation. CL has earlier been reported to have a single pK at low pH. We have titrated CL in aqueous suspension (bilayers) and in solution in methanol/water (1:1, vol/vol) and found it to display two different pK values, pK1 at 2.8 and pK2 initially at 7.5 but shifting upwards to 9.5 as the titration proceeds. The unusually high pK2 Might be explained by the formation of a unique hydrogen bond in which the free hydroxyl on the central glycerol forms a cyclic intramolecular hydrogen-bonded structure with one protonated phosphate (P-OH group). We have therefore chemically synthesized the 2'-deoxycardiolipin analogue, which lacks the central free hydroxyl group, and measured its pH-dissociation behavior by potentiometric titration, under the same conditions as those for CL. The absence of the hydroxyl group changes the titration dramatically so that the deoxy analogue displays two closely spaced low pK values (pK1 = 1.8; pK2 = 4.0). The anomalous titration behavior of the second dissociation constant of CL may be attributed to the participation of the central glycerol OH group in stabilizing the formation of a cyclic hydrogen-bonded monoprotonated form of CL, which may function as a reservoir of protons at relatively high pH. This function may have an important bearing on proton pumping in biological membranes.