Reevaluation of the phospholipid composition in membranes of adult human lenses by 31P NMR and MALDI MS

The phospholipid composition of adult human lens membranes differs dramatically from that of any other mammalian membrane. Due to minimal cell turnover, cells in the nucleus of the human lens may be considered as the longest lived cells in our body. This work reassesses previous assignments of phospholipid 31P NMR resonances in adult human lenses. The new assignments are based not only on chemical shifts but also on temperature coefficients. By addition of known phospholipids and examination by matrix-assisted laser desorption/ionization mass spectrometry, several misassigned resonances have been corrected. The revised composition reveals the possible presence of ceramide-1-phosphate and dihydroceramide-1-phosphate. Among glycerophospholipids, the most abundant one does not correspond to phosphatidylglycerol but may be due to the lysoform of alkyl–acyl analogs of phosphatidylethanolamine. Besides sphingophospholipids, adult human lens membranes contain significant amounts of ether (1-O-alkyl) glycerophospholipids and their corresponding lysoforms.