Arrangement of phosphatidylserine and phosphatidylethanolamine in the erythrocyte membrane.

Cross-linking of phosphatidylethanolamine and phosphatidylserine in the erythrocyte membrane with the reagent difluorodinitrobenzene was studied as a function of temperature, time and concentration of difluorodinitrobenzene. The optimal extent of cross-linking of phosphatidylethanolamine to phosphatidylethanolamine, phosphatidylethanolamine to phosphatidylserine and phosphatidylserine to phosphatidylserine was expressed as molar ratios of these three different cross-linked species. The experimental results were compared to different models of a phospholipid monolayer containing phosphatidylethanolamine and phosphatidylserine in which phosphatidylserine was arranged primarily as singles (having 6 phosphatidylethanolamine neighbors) as clusters of dimers, trimer and tetramers or as large clusters. In the various model monolayers each lipid component has 6 neighbors. The models which are consistent with the experimental results are those in which phosphatidylserine and phosphatidylethanolamine occur as small clusters in a non-random array.