Proton Magnetic Resonance Studies of Membrane Systems. I. Effect of Sonication and Osmotic Pressure on the Structure of the Lecithin Bilayer. II. PMR study of the Human Erythrocyte Membrane upon Perturbation.

Citation

Sheetz, Michael Patrick (1973) Proton Magnetic Resonance Studies of Membrane Systems. I. Effect of Sonication and Osmotic Pressure on the Structure of the Lecithin Bilayer. II. PMR study of the Human Erythrocyte Membrane upon Perturbation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ZPAB-K217. https://resolver.caltech.edu/CaltechTHESIS:07202018-112502895

Abstract

I. Effect of Sonication and Osmotic Pressure on the Structure of the Lecithin Bilayer

The properties of dipalmitoyl lecithin vesicles of varying sizes have been compared employing proton and ³¹P nmr spectroscopy and dilatometry. These studies indicate that small vesicles of about 250 Å in diameter are inherently disordered and that the well-known spectral differences generally observed for vesicles of different curvatures, such as lecithin multilayers and sonicated bilayers, arise from variations in the molecular packing of phospholipid molecules in the bilayer phase. Upon further perturbation of the membrane by an external osmotic pressure spectral changes were noted which were consistent with the expected changes in molecular packing. It was also noted that the structural rigidity of the bilayer appeared to change upon melting.

II. PMR Study of the Human Erythrocyte Membrane upon Perturbation

An analysis of the pmr spectra of human erythrocyte membranes has been made in terms of the membrane components. The spectrum at 75° was assigned to 20% of the membrane proteins, 20% of the choline methyl groups of the phospholipids, and the acetamide groups of the sugars. Changes in the pmr spectra were noted when the membranes were altered by either protein solubilization or membrane fragmentation. The choline methyl signal was found to be particularly sensitive to the state of the membranes. Certain proteins were found to be released from the membranes at high temperatures and this phenomenon was dependent upon the pH and the solvent, as well as the presence of certain ions in solution. The amount of proteins solubilized, however, was significantly less than that observed by the high-resolution pmr method. The effect of certain divalent ions was particularly striking. The presence of more than 5 x 10^-4 M Mg²⁺, for example, was sufficient to stabilize the proteins in the membrane and eliminate the high-resolution pmr signal.

B. cereus and Cl. perfringens phospholipase C treatments were found to have quite different effects on human erythrocyte membranes from the pmr spectra of the treated membranes. These differences are explained in terms of the properties of the unreacted lipids left by the two enzymes.

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