We studied the conformation of the membrane skeleton of human red blood cells (RBC) after detergent extraction of RBC ghosts, using video microscopy, light scattering, and synchrotronbased small angle X-ray scattering (SAXS). RBC membrane skeletons are two-dimensionally connected, triangulated networks of flexible, polyionic proteins. Immediately after extraction, the skeletons exhibited large-scale thermal undulations and deformed strongly in weak shear flow. Screening of electrostatic repulsion by immersion in high ionic strength buffer led to shrinkage, while the shell-like conformations and the flexibility of the skeletons were preserved. Under high ionic strength conditions (1 M monovalent salt), the static structure factor, S(q), showed two power law regimes S(q) ∝ q −α, with α <≈ 2.0 in the range of wave vectors 4×10−4 Å−1 < g < 8×10−4 Å−1, and α = 2.3 ± 0.1 in the range of wave vectors 8×10−4 Å−1 < q < l×10−1 Å−1. The same power law behavior was observed in low ionic strength buffer (25 mM salt) for q < 2×10−3 Å−1. This result is not consistent with the occurence of a crumpling transition during skeleton shrinkage. The observed form of the static structure factor, with a transition between two regimes with different power law exponents, presents evidence for the theoretically predicted flat phase of 2D-polymers.
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