Solubilization of human erythrocyte membrane glycoproteins by triton X-100

Kinetic evidence for modulation by glycophorin A of a conformational equilibrium between two states of band 3 (SLC4A1) bound reversibly by the competitive inhibitor DIDS

Recent evidence has suggested that erythrocytes naturally deficient in glycophorin A (GPA) have a reduced V(max) for monovalent anion exchange. Unanswered is whether miss-folding of band 3 during biosynthesis, or the absence of GPA modulation of properly folded band 3 is responsible. Here, I determine the effect of selective depletion of GPA on the kinetics of reversible binding of the competitive transport inhibitor DIDS (4,4'-diisothiocyanato-2,2'-stilbenedisulfonate) to properly folded band 3. Reversible binding of DIDS follows biphasic kinetics: a fast phase {DIDS+band 3<-->(DIDS-band 3), k(1), k(-1)} and a slower phase {(DIDS-band 3)<-->(DIDS-band 3), k(2), k(-2)}. Selective depletion of GPA was accomplished by pretreating membranes with Triton X-100, over a range where erythrocyte hemolysis is inhibited by the detergent (0% to 0.03%, v/v). Pretreatment with sublytic Triton X-100: (a) virtually completely depleted GPA, (b) did not deplete membrane-bound band 3, and (c) slowed the overall rate of reversible binding of DIDS to band 3. Data analysis and model simulation studies indicated that the decrease in the rate of binding of DIDS was due exclusively to a decrease in k(-2), with no change in the initial rate of binding. Thus, depletion of GPA does not alter the native conformation of band 3 at the DIDS binding site, but rather modulates a conformational equilibrium between two states of the binary complex formed by the competitive inhibitor DIDS, reversibly bound to properly folded band 3.

Isolation from chick somites of a glycoprotein fraction that causes collapse of dorsal root ganglion growth cones

The segmented pattern of peripheral spinal nerves in higher vertebrates is generated by interactions between nerve cells and somites. Neural crest cells, motor axons, and sensory axons grow exclusively through anterior-half sclerotome. In chick embryos, posterior cells bind the lectins peanut agglutinin (PNA) and Jacalin. When liposomes containing somite extracts are applied to cultures of chick sensory neurons, growth cones collapse abruptly, recovering within 4 hr of liposome removal. Collapse activity is eliminated by immobilized PNA, and SDS-PAGE demonstrates two major components (48K and 55K), which are absent from anterior-half sclerotome. Rabbit polyclonal antibodies against these components recognize only posterior cells and may also be used to eliminate collapse activity. We suggest that spinal nerve segmentation is produced by inhibitory interactions between these components and growth cones.

The relationship of detergent-solubilization plasma-membrane components of rabbit alveolar macrophages to an isolated inhibitor of phagocytosis

1. A plasma-membrane fraction prepared from rabbit alveolar macrophages by hyposmotic borate lysis is described. 2. Rabbit lung lavages, containing a glycoprotein inhibitor of phagocytosis, may be fractionated by preparative isoelectric focusing in the presence of Triton X-100. 3. Chemical analysis indicates that the glycoproteins of the lung lavage contain sialic acid, fucose, mannose, galactose, hexosamine and appreciable quantities of glucose. 4. The relationship of macrophage membrane glycoproteins, solubilized with Triton X-100 in the presence of borate, to the lung lavage glycoproteins is demonstrated immunoelectrophoretically.