Spin-label studies on rat liver and heart plasma membranes: Do probe-probe interactions interfere with the measurement of membrane properties?

Summary The structures of purified rat liver and heart plasma membranes were studied with the 5-nitroxide stearic acid spin probe,I(12, 3). ESR spectra were recorded with a 50 gauss field sweep, and also with a new technique which “expands” the spectrum by (1) recording pairs of adjoining peaks with...
Ausführliche Beschreibung

Summary The structures of purified rat liver and heart plasma membranes were studied with the 5-nitroxide stearic acid spin probe,I(12, 3). ESR spectra were recorded with a 50 gauss field sweep, and also with a new technique which “expands” the spectrum by (1) recording pairs of adjoining peaks with a smaller field sweep and (2) superposing the common peaks. The hyperfine splittings measured from the “expanded” spectra were significantly more precise than those obtained from the “unexpanded” spectra. Both procedures were used to study the effects of variousI(12,3) prove concentrations on the spectra of liver and heart membranes, as well as the effects of temperature and $ CaCl_{2} $ additions on the spectra of liver membranes, and revealed the following: The polarity-corrected order parameters of liver (31°) and heart (22°) membranes were found to be independent of the probe concentration, if experimentally-determined lowI(12,3)/lipid ratios were employed. The absence of obvious radical-interaction broadening in the unexpanded spectra indicated that “intrinsic” membrane properties may be measured at these low probe/lipid ratios. Here, “intrinsic” properties are defined as those which are measured when probe-probe interactions are negligible, and do not refer to membrane behavior in the absence of a perturbing spin label. At higherI(12,3)/lipid ratios, the order parameters of liver and heart membranes were found to substantially decrease with increasing probe concentration. The increase in the “apparent” fluidity of both membrane systems is attributed to enhanced radical interactions; however, an examination of these spectra (without reference to “low” probe concentration spectra) might incorrectly suggest that radical interactions were absent. For the membrane concentrations employed in these studies, the presence of “liquid-lines” (or “fluid components”) in the unexpanded ESR spectra was a convenient marker of high probe concentrations. A thermotropic phase separation was observed in liver membranes between 19° and 28°. Addition of $ CaCl_{2} $ to liver plasma membrane [labelled with “low”I(12,3) concentrations] increased the rigidity of the membrane at 31° and 37°, without inducing a segregation of the probe in the bilayer. Previously reported data are discussed in relation to these results, and suggested minimal criteria for performing membrane spin label studies are included. Ausführliche Beschreibung

Autor*in:	Sauerheber, Richard D. [verfasserIn] Gordon, Larry M. Crosland, Richard D. Kuwahara, Melvin D.

Format:	E-Artikel
Sprache:	Englisch

Erschienen:	1977

Schlagwörter:	Nitroxide Spin Label Spin Probe Probe Concentration Hyperfine Splitting

Anmerkung:	© Springer-Verlag New York Inc 1977

Übergeordnetes Werk:	Enthalten in: The journal of membrane biology - New York, NY : Springer, 1969, 31(1977), 1 vom: Dez., Seite 131-169
Übergeordnetes Werk:	volume:31 ; year:1977 ; number:1 ; month:12 ; pages:131-169

Links:	Volltext

DOI / URN:	10.1007/BF01869402

Katalog-ID:	SPR00264584X