A new and simple approach for the determination of the temperature of gel-to-liquid crystalline phase transitions (Tc) of biological (chloroplast) membrane lipids from 13C-NMR resonance intensities is proposed. The variation of intensity of a temperature-sensitive NMR resonance is monitored by recording the spectra of the sample at a range of temperatures. From such a series of spectra recorded at different temperatures, a temperature-insensitive resonance is located. Then the ratio of the intensity of the temperature-sensitive to the intensity of the temperature-insensitive resonance is calculated from each spectrum to even out the procedural error, if any. The values of this ratio at different temperatures, when plotted against sample temperature, shows a break at Tc as confirmed by spin label ESR studies.
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[Show abstract][Hide abstract] ABSTRACT: Spinach chloroplast membranes and aqueous dispersions of their extracted lipids have been studied by spin label (stearic acid)
electron spin resonance and carbon-13 nuclear magnetic resonance techniques. Combined with electron microscope studies, first
systematic evidence is found for the existence of a dynamic lipid-bilayer structure in the chloroplast membranes.
Journal of Biosciences 12/1990; 15(4):281-288. DOI:10.1007/BF02702669 · 2.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Spinach chloroplast membranes labelled with stearic acid-spin probe-bearing nitroxyl (label) moiety at 5th, 9th, 12th, 13th, 14th or 16th carbon locations with respect to the carboxylic group of stearic acid were studied (in the dark) by electron spin resonance (ESR) spectroscopy. Spectra were recorded at sample temperatures of 5, 30 and 67 degrees C. After heat denaturation of the membrane proteins for 5 min at 67 degrees C, the spectra were re-recorded at 30 and 5 degrees C for comparison. The results unequivocally show that membrane lipid fatty-acyl chains become substantially more rigid after protein heat-denaturation. The data throw light on the degree of lipid-protein interactions at various microlocations along the length of fatty-acyl chains of the membrane lipid matrix.
Journal of Biochemical and Biophysical Methods 02/1991; 22(1):55-9. DOI:10.1016/0165-022X(91)90081-7 · 1.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Employing negative-staining electron microscopy, convincing evidence has been obtained for the destabilisation of multilamellar organisation of aqueous dispersions of chloroplast thylakoid membrane lipids, to an inverted micellar structure under the influence of sucrose solution. The present study provides a new insight into the phase behaviour of a naturally existing galactolipid-rich lipid mixture consequent to interaction with a kosmotropic reagent.