PubMed · 2095867
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Z S Toktamysova, N Kh Birzhanova. [Membrane bound hemoglobin].. https://pubmed.ncbi.nlm.nih.gov/2095867/
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In order to morphologically characterize exo- and endovesicles released during treatment of erythrocytes with amphiphiles and to look for possible amphiphile-specific effects on the vesiculation pattern, human erythrocytes were treated at 37 degrees C with amphiphiles at concentrations where they exhibit maximum protection against hypotonic haemolysis (cAHmax). Released exo-and endovesicles and treated cells were studied by means of transmission (TEM) and scanning (SEM) electron microscopy. All sphero-echinocytogenic amphiphiles induced a release of both spherical and tubular exovesicles. Dodecyl maltoside, a nonionic amphiphile with a bulky polar head, induced a release of predominantly tubular exovesicles, while all other sphero-echinocytogenic amphiphiles induced a release of predominantly spherical exovesicles. Some branched tubular exovesicles were released by a double-chained cationic amphiphile. Tail- and tongue-like structures were often seen on the exovesicles. Spherical exovesicles were frequently invaginated. Stomatocytogenic amphiphiles induced endovesiculation. In erythrocytes treated with most of the stomatocytogenic amphiphiles the endovesicles were clustered, but with some amphiphiles the endovesicles were randomly distributed. Large ringformed endovesicles (octaethyleneglycol alkyl ethers) and endovesicles in chains (octyl and decyl glucopyranoside) also occurred. The endovesicle membrane was often budding onto the lumen of the vesicle and in some cases this could ultimately lead to a vesicle inside the endovesicle. We conclude that amphiphiles do not only trigger vesiculation, but may also specifically affect the vesiculation processes.
The main objective of depth-dependent fluorescent probes is to provide information at a distinct position in the membrane hydrophobic core. We report here a series of fluorenyl fatty acids which can probe both artificial and natural membranes at different depths. Long-chain acids (C4, C6, and C8) are attached to fluorene chromophore on one side, and a hydrophobic tail (C4) is attached on the other side, so that on incorporation in membranes the carboxyl end of the molecule is oriented toward the membrane-water interface and the hydrophobic tail points toward the membrane interior. These acids can be readily partitioned into membranes. The disposition of these fluorenyl fatty acids in membranes was studied by fluorescence quenching using iodide as a water-soluble and 9,10-dibromostearic acid as a lipid-soluble quencher. The results obtained indicate that attachment of a hydrophobic tail is essential for effective alignment of depth-dependent fluorescent probes. The length of the hydrophobic tail was varied and an n-butyl chain was found to be most effective. In all cases, the compounds with a hydrophobic tail were found to be probing the membrane deeper than their counterparts with no hydrophobic tail. Further, the compounds with hydrophobic tails were more strongly immobilized in the membrane as indicated by fluorescence polarization studies. However, the effect of such a tail varied with membrane type. Thus in artificial membranes an n-butyl chain was found to be extremely important for effective monitoring by shallow probes like 4-(2'-fluorenyl)butyric acid, whereas in erythrocyte ghost membranes the same n-butyl tail was found to be more desirable for deeper probes like 8-(2'-fluorenyl)octanoic acid.(ABSTRACT TRUNCATED AT 250 WORDS)
The self-association of human spectrin has been studied by means of sedimentation equilibrium in the analytical ultracentrifuge at pH 7.5 and over a range of ionic strength from 0.009 to 1.0 M. Increasing ionic strength above 0.1 M reduces the equilibrium constants for all of the measurable steps in the self-association reaction. These results support the concept of charge-charge interactions stabilizing the tetramer and higher oligomers with respect to the heterodimer. In addition, increasing ionic strength brought about a dissociation of the heterodimer to component polypeptide chains. Dissociation to the heterodimers is also enhanced with a decrease in ionic strength below 0.05 M. This low ionic strength-dependent dissociation is consistent with generalised electrostatic repulsion; however, this effect also correlates with some loss of alpha-helical content as revealed by circular dichroism. The secondary, tertiary and quaternary structures may all be partially disrupted by electrostatic free energy at low ionic strength.