Evidence from dielectric studies for the presence of bound water in myelin

Gent, W. L. G.; Grant, E H; Tucker, S. W.

doi:10.1002/bip.1970.360090112

Cited by 15 publications

(5 citation statements)

References 6 publications

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“…In this connection, it is worthwhile to note the dielectric studies of Gent et al (1970), who reported the presence of highly organized water of "ice-like" character in myelin, comparable to biological interfacial water (Kuntz & Kauzmann, 1974). Finally, it is interesting that the other major protein of myelin, the Folch-Pi proteolipid, which is insoluble in aqueous solvents, also displays optimal solubilization in reverse micelles at the low value of w0 = 5.6 (Delahodde et al, 1984).…”

Section: Discussionmentioning

confidence: 88%

Membrane proteins as reverse micelles: myelin basic protein in a membrane-mimetic environment

Nicot¹,

Vacher²,

Vincent³

et al. 1985

Biochemistry

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The solubility, reactivity, and conformational dynamics of myelin basic protein (MBP) from bovine brain were studied in reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT)-isooctane and water. Such a membrane-mimetic system resembles the aqueous spaces of native myelin sheath in terms of physicochemical properties as reflected in the high affinity of MBP for interfacial bound water. This is marked by the unusual profile of the solubility curve of the protein in reverse micelles, which shows optimal solubility at a much lower molar ratio of water to surfactant ([ H2O]/[AOT] = w0) than that reported for other water-soluble proteins. The role of counterions and/or charged polar head groups in the solubilization process is revealed by comparison of the solubility of MBP in nonionic surfactant micellar solutions. Whereas MBP is unfolded in aqueous solutions, insertion into reverse micelles generates a more folded structure, characterized by the presence of 20% alpha-helix. This conformation is unaffected by variations in the water content of the system (in the 2.0-22.4 w0 range). The reactivity of epsilon-amino groups of lysine residues with aqueous solutions of o-phthalaldehyde demonstrates that segments of the peptide chain are accessible to water. Similar results were obtained with the sequence involved in heme binding. In contrast, the sole tryptophan residue, Trp-117, is shielded from the aqueous solvent, as indicated by lack of reaction with N-bromosuccinimide. The invariance of the wavelength maximum emission in the fluorescence spectra as a function of w0 is consistent with this result.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Discussionmentioning

confidence: 88%

Membrane proteins as reverse micelles: myelin basic protein in a membrane-mimetic environment

Nicot¹,

Vacher²,

Vincent³

et al. 1985

Biochemistry

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“…Another explanation is suggested by recent dielectric measurements (Gent, Grant and Tucker 1970) on purified myelin suspensions extracted from brain white matter, which show an unexpectedly low permittivity near 1 GHz. These authors attributed this effect to a 'bound water' fraction which does not contribute significantly t'o the sample polarisation in this frequency range, The discrepancy between our calculated tissue water fractions and the literature values is removed by assuming a 'bound water' fraction of 0.5 cm3 per cm3 of solid matter, intermediate between 'bound water' fractions suggested for protein solutions (Cooke and Kuntz 1974) and for myelin suspensions (Gent et al 1970) (Table 1 ) . In other respects, the dielectric properties of the nonliving tissue studied here are a's expected of a suspension of nonconducting, low permittivity material in normal 'bulk' wat'er.…”

Section: Discussionmentioning

confidence: 93%

Dielectric properties of brain tissue between 0.01 and 10 GHz

Foster

Schepps

Stoy

et al. 1979

pmb

152

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Dielectric permittivity and conductivity are reported for grey and white matter from dog brain tissue between 0.01 and 10 GHz. Between 0.01 and approximately 1 GHz, the permittivity decreases and conductivity increases as a power law of frequency. Above 1 GHz, the conductivity increases quadratically with frequency due to dipolar reorientation of free water molecules in tissue; the apparent rotational relaxation frequency at 37 degrees C is 21--25 GHz, slightly below the 25 GHz characteristic frequency of pure water at that temperature. The microwave data are analysed using the Maxwell mixture theory applicable for a suspension of nonconducting, low permittivity spheres in bulk water. From the increase in conductivity above 1 GHz, and the tissue permittivity at 2--4 GHz, the apparent volume fraction of water is approximately 0.70 and 0.55 for grey and white matter, respectively, about 10--15% lower than respective values from the literature. This discrepancy is apparently due to a small fraction of water which does not contribute to the tissue permittivity above 1 GHz. Empirical equations are given to summarise the dielectric properties of 'average' brain tissue at 37 degrees C for future theoretical studies of microwave absorption in the head.

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“…Other measurements on membranes include early work by Waugh and Schmitt [39] who obtained a value of about 30 to 40 % water per dry weight of erythrocyte membranes from reflectivity measurements (leptoscope), and Ponder [29], who measured the hematocrit volume of rehydrated erythrocyte ghosts and estimated that they contained 200 g H20/100 g dry membranes. Gent, Grant and Tucker [20] have found by dielectric measurements that in myelin a minimum of 100 g H20/100 g dry weight is sufficiently bound so that it is not free to rotate in an dectric field at high frequencies. Ladbrooke and Chapman [27], using calorimetric methods, found that in myelin below about 25 % hydration (with respect to dry weight), the thermal transition for liquid water to ice disappears and endothermic transitions (35, 55 ~ of the cholesterol and phospholipids appear.…”

Section: Discussionmentioning

confidence: 98%

Water in biological membranes: Adsorption isotherms and circular dichroism as a function of hydration

Schneider

1972

J. Membrain Biol.

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Adsorption isotherms of water on human red cell membranes have been measured and the results used to determine the Brunauer-Emmett-Teller monolayer coverage, saturation hydration, and relevant heats and entropies of hydration. The tightly bound monolayer corresponds to a complete covering of only one membrane surface and the saturation hydration is greater than values for globular proteins and phospholipids. A hysteresis loop is observed in the adsorption-desorption cycle.Circular dichroism spectra of membrane films have been measured as a function of hydration in the ultraviolet region of the spectrum. The spectra resemble those of membrane suspensions with reduced scattering. The circular dichroism did not change upon dehydration of the membrane films from 92 to 0% relative humidities, implying a stable membrane protein structure independent of both water content and lipid phase.

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Evidence from dielectric studies for the presence of bound water in myelin

Cited by 15 publications

References 6 publications

Membrane proteins as reverse micelles: myelin basic protein in a membrane-mimetic environment

Membrane proteins as reverse micelles: myelin basic protein in a membrane-mimetic environment

Dielectric properties of brain tissue between 0.01 and 10 GHz

Water in biological membranes: Adsorption isotherms and circular dichroism as a function of hydration

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