An electro-optic study of human erythrocyte spectrin dimers. The presence of calcium ions does not alter spectrin flexibility.

In order to determine whether the presence of Ca2+ increases the stiffness of the highly elongated and flexible spectrin molecules, we have carried out a birefringence relaxation study of isolated human erythrocyte spectrin dimers. Our measurements indicate no significant change in the flexibility of spectrin in solutions containing 0-10(-3) M Ca2+. This finding indicates that decreased spectrin flexibility is not the major functional mechanism underlying the decreased erythrocyte deformability reported as result of elevated intracellular levels of Ca2+. We find that the persistence length of spectrin dimers is less than 20 nm and is not dependent on the Ca2+ concentration.