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Mixed‐chain phospholipids: Structures and chain‐melting behavior
Author(s) -
Huang Chinghsien
Publication year - 2001
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/s11745-001-0818-1
Subject(s) - degree of unsaturation , differential scanning calorimetry , methylene , chain (unit) , chemistry , phosphatidylethanolamine , double bond , phosphatidylcholine , crystallography , organic chemistry , phospholipid , thermodynamics , membrane , biochemistry , physics , astronomy
It has long been established that diacyl phospholipids isolated from animal cell membranes are predominantly of a mixed‐chain variety, meaning that the sn ‐1 and sn ‐2 acyl chains are saturated and unsaturated acyl chains, respectively. In general, monoenoic and dienoic acids are found in the sn ‐2 acyl chain of phosphatidylcholine (PtdCho), whereas polyenoic acids are in phosphatidylethanolamine (PtdEth). These unsaturated chains contain only cis ‐double bonds, which are always methylene‐interrupted. In recent years, the structures and the chain‐melting behavior of mixed‐chain PtdCho and PtdEth have been systematically studied in this laboratory. Specifically, we have examined the effects of chain unsaturation of the sn ‐2 acyl chain on the phase transition temperature (T m ) of many PtdCho and PtdEth by high‐resolution differential scanning calorimetry (DSC). The T m values, for instance, obtained from all‐unsaturated mixed‐chain PtdEth derived from a common precursor can be grouped together according to their chemical formula to form a T m ‐diagram. Hence, all the T m values can be compared simply, systematically, and simultaneously using the T m ‐diagram. In addition, the energy‐minimized structures of mixed‐chain phospholipids containing different numbers/positions of methylene‐interruped cis ‐double bonds have been simulated by molecular mechanics calculations (MM). In this review, the results of our MM and DSC studies carried out with various mixed‐chain phospholipids are summarized. In addition, we emphasize that the combined approach of MM and DSC yields unique uniformation that can correlate the various T m ‐profiles seen in the T m ‐diagram with the structural variation of mixed‐chain lipids as caused by the introduction of different numbers/positions of methylene‐interrupted cis ‐double bonds.