Do superlattices exist in biological membranes?
For the biologist the key questions are whether superlattices exist in biological membranes and if so, what their functional relevance is. Regarding the former issue, we have recently observed that the previously published phospholipid compositions of mammalian red cell membranes generally fall close to critical compositions predicted by a model assuming that the phospholipid tend to adopt a regular, superlattice-like distribution in both membrane leaflets [59]. This model makes the simplifying assumption that the erythrocyte phospholipids can be divided into three groups of equivalent species according to the head group: (1) the choline phospholipids (CPs), i.e. SM, PC and LPC; (2) the acidic phospholipids (APs), i.e. PS, PI and PA; and (3) the ethanolamine phospholipids, i.e. PE and its ether derivatives. For such a ternary system the critical concentrations of the components are multiples of 11.1 mole%, i.e. 0, 11.1, 22.2, 33.3, 44.4 mole% etc. [59]. Table 1 displays the observed an
