Freeze-etching and biochemical analysis of human fetal erythrocyte membranes.

In order to test the hypothesis that there are ultrastructural and supramolecular differences between fetal and adult erythrocyte membranes that are manifested in their functional characteristics, the cells were studied by freeze-etching and transmission microscopy and biochemical methods. Freeze-etching and transmission electron microscopy of fetal erythrocyte membranes showed that the protoplasmic and exoplasmic fracture faces have 24% and 45% greater intramembrane particles respectively compared to adult cells (p less than 0.01). The apparent diameters of the intramembrane particles estimated on the exoplasmic fracture face averaged as follows: 4.84, 7.74, 11.42, and 15.64 nm, which are similar to estimates in adult cell membranes, suggesting similar dimensions for the presumptive glycoprotein structures in the fluid mosaic complex of the cell membranes. The average total cholesterol, phospholipid, and protein content per fetal erythrocyte ghost as well as ratios of protein/lipid, protein/cholesterol, and protein/phospholipids were all significantly greater than in the adult ghost (p less than 0.01). Analysis of fetal and adult ghost proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed similar qualitative and quantitative polypeptide and glycopeptide bands except for the intense appearance of bands 4.5 and 8 in the fetal samples. Polypeptide chains per ghost membrane were significantly greater in fetal ghosts than in adult ghosts. However, the molar ratios of the major polypeptides relative to band 3, the predominant protein in the ghost membrane, are comparable for the two cell types except for bands 4.5 and 8. These findings suggest that the molecular characteristics of the erythroid plasma membrane vary with the developmental age.