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The pK's of Cardiolipins Are Altered by the Number and Position of their Specific Fatty Acid Esters
Author(s) -
Haines Thomas H.,
Epand Richard,
Epand Raquel
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.632.1
Subject(s) - cardiolipin , cardiolipins , chemistry , titration , stereochemistry , membrane , fatty acid , pi , crystallography , biochemistry , phospholipid , organic chemistry
We’ve confirmed that the 2 phosphate groups of tetrastearoyl‐cardiolipin (CL) have distinctly different pK values, one above neutrality. Although CL's chemical structure, suggests that it has 2 identical negative charge at neutral pH, our data shows it does not. Previously (Kates et al. (1993) Lipids , 28 , 877–882), showed the pK 2 was >8.0 with the tetrastearoyl CL, we have examined the dependence of the titration of cardiolipin on the number and nature of the acyl chains. The high pK 2 varies, with the chainlength and desaturation of the chains on the lipid. As the chain structure is varied, the pK 2 ranges from 3–8. The latter dominates with C 18 chains. Short chains yield lower pK 2 's e.g., E. coli CL. Typical mitochondrial CL's have 4 linoleoyl chains. The high pK 2 is explained by a bicyclic, H‐bonded conformation of CL's headgroup. Evidence for this has been provided by showing that deoxycardiolipin, lacking the central OH of the connecting glycerol, has a pK 2 below 4.0. This data supports the proposal that CL has a role in ATP synthesis by providing a pool of protons on both sides of the membrane for proton pumping (Haines & Dencher (2003) FEBS Lett. 528 , 35–39). Our results show the high pK 2 , present in tetramyristoyl cardiolipin is missing in myristoyl lysocardiolipin. A chemical test for the often fatal Barth's Syndrome is lysocardiolipin. Our results may be relevant to this genetic disease which may have defective ATP synthesis.