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Hemoglobin enhances the self-association of spectrin heterodimers in human erythrocytes.

1984; Elsevier BV; Volume: 259; Issue: 18 Linguagem: Inglês

10.1016/s0021-9258(18)90898-7

1083-351X

S C Liu, J Palek,

Pancreatic function and diabetes

Spectrin in isolated erythrocyte membranes is known to undergo tetramer to dimer transformation upon hypotonic incubation at 37 OC.In the present study, we detect no such transformation in intact erythrocytes in which hypotonicity is achieved by valinomycin treatment followed by hypotonic swelling.The inhibition of spectrin tetramer to dimer transformation is attributable to intracellular hemoglobin, since the addition of hemoglobin to isolated membranes or spectrin extracts blocks a similar spectrin transformation.However, the inhibitory effect is not limited to hemoglobin; other proteins including heme-containing proteins and basic proteins such as cytochrome e, ribonuclease, and albumin are also effective.The magnitude of their effect is proportional to the increased PI value of these proteins.We conclude that the stabilizing effect of these proteins on spectrin tetramers under hypotonic conditions is partly due to their nonideality, which excludes water from spectrin and thus increases the effective concentration of spectrin, and to their electrostatic interactions with spectrin.In addition, promotion of spectrin self-association by hemoglobin under hypotonic conditions increases the stability of membrane skeletons against mechanical shearing.More importantly, the hemoglobin effect on spectrin self-association is demonstrable at physiological hemoglobin concentration, pH, and osmolarity, suggesting that in intact red cells the spectrin dimer-dimer association, as well as the membrane skeletal structure, is strengthened by intracellular hemoglobin.Spectrin, the major protein of the red cell membrane skeleton, is composed of two nonidentical subunits (a chain, 240,000 Da, and /3 chain, 220,000 Da) which are associated into double-stranded, fiber-like flexible heterodimers about 100 nm in length (for review, see Refs.1-4).In normal red cells, SpD' are assembled, head to head, into SpT and higher order oligomers.These species are interconnected in a continuous submembrane network by their interaction with oligomeric actin, which binds to the distal ends of the bifunctional SpT.This interaction is markedly enhanced by protein 4.1 (M, = 78,000) which binds to the distal ends of SpT and greatly strengthens their interaction with actin.