Premium
pH‐dissociation characteristics of cardiolipin and its 2′‐deoxy analogue
Author(s) -
Kates Morris,
Syz JingYi,
Gosser David,
Haines Thomas H.
Publication year - 1993
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02537494
Subject(s) - chemistry , cardiolipin , titration , potentiometric titration , titration curve , protonation , membrane , dissociation constant , dissociation (chemistry) , intramolecular force , hydrogen bond , aqueous solution , inorganic chemistry , medicinal chemistry , stereochemistry , organic chemistry , phospholipid , molecule , biochemistry , ion , receptor
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, pK 1 at 2.8 and pK 2 initially at 7.5 but shifting upwards to 9.5 as the titration proceeds. The unusually high pK 2 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 (pK 1 =1.8; pK 2 =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.