Divalent cation binding to erythrocyte spectrin
C J Wallis1, J A Babitch, E F Wenegieme
1Department of Chemistry, Texas Christian University, Forth Worth 76129.
Abstract:
Erythrocyte spectrin dimers and separated alpha- and beta-spectrin chains bound 45Ca2+ after electrophoresis on native or sodium dodecyl sulfate-polyacrylamide gels, blotting, and 45Ca2+ overlay. Flow dialysis and equilibrium dialysis revealed two binding components: high-affinity, Ca(2+)-specific sites with kd = 4 x 10(-7) M and n = 100 +/- 20 per dimer and a low-affinity (millimolar) divalent cation component. Whereas brain spectrin had only four high-affinity sites [Wallis, C. J., Wenegieme, E. F., & Babitch, J. A. (1992) J. Biol. Chem. 267, 4333-4337], erythrocyte spectrin had 25-fold more sites per dimer. In addition to possibly modifying spectrin interactions with calcium-dependent protease and actin, as suggested by previous work on the interaction of Ca2+ with brain spectrin, the approximately two high-affinity sites per repeating segment of erythrocyte spectrin appear to stabilize a folded conformation of repeat structures indicated by an entropy increase upon binding. These data support the hypothesis that divalent cation binding to erythrocyte spectrin has become specialized to stabilize the membrane skeletal network and the cell, making them flexible but resistant to shear under the stressful conditions of blood circulation.
Related Concept Videos
02:42Valence Bond Theory
01:30Drug Binding to Blood Components
HSA is the most abundant plasma protein and is vital in drug binding. It contains distinct drug-binding sites, with different drugs exhibiting affinity for specific sites. There are three main drug-binding domains for HSA: sites I, II, and III. These domains are further...
01:22EDTA: Chemistry and Properties
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...