CONFORMATIONAL ORDER OF SPECIFIC PHOSPHOLIPIDS IN HUMAN ERYTHROCYTES - CORRELATIONS WITH CHANGES IN CELL-SHAPE

Acyl chain perdeuterated dimyristoylphosphatidylcholine (DMPC-d(54)) a nd dimyristoylphosphatidylserine (DMPS-d(54)) were incorporated into h uman erythrocytes. Light microscopy demonstrated that erythrocytes inc ubated with an equimolar mixture of DMPC-d(54)/DMPS or DMPC/DMPS-d(54) remained mostly discocytic whereas cells incubated with either DMPC-d (54) or DMPS-d(54) alone became echinocytic or stomatocytic, respectiv ely. Cells in which the aminophospholipid translocating protein was in hibited became echinocytic when incubated with DMPS-d(54). Fourier tra nsform infrared (FTIR) spectroscopy was used to monitor conformational order in the acyl chains of the incorporated phospholipid, as detecte d through the asymmetric CD2 stretching vibrations in the intact cells . In cells incubated with equimolar mixtures of DMPC-d(54)/DMPS or DMP C/DMPS-d(54), the deuterated species exhibited no thermotropic phase t ransitions but revealed chain order intermediate between the gel and l iquid-crystal states. In contrast, DMPS-d(54) incorporated into the ou ter leaflet of echinocytic erythrocytes was conformationally ordered w hile the same species incorporated into the inner leaflet of stomatocy tic erythrocytes was highly disordered at all temperatures studied. Fi nally, DMPC-d(54) incorporated into the outer leaflet of echinocytic e rythrocytes exhibited a phase transition, suggesting that this species persists in domains. These data indicate that the acyl chain conforma tional order of specific phospholipids in the intact human erythrocyte is changed with alterations in cell morphology.