Bertoli, E. (1975) Membrane fluidity and functional organization of the mitochondrial membranes. PhD thesis, University of Warwick.

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Abstract

Fluidity, existence of phase transitions and structural organization of lipoproteins in Saccharomyces cerevisiae promitochondria has been investigated by means of X-ray diffraction, differential scanning calorimetry, spin label techniques and freeze-etching.

Distinct phase transitions were found with these organelles which were shown to be partly dependent upon the lipid composition of the membranes.

X-ray diffraction patterns from these membranes show that two physical states of lipids were distinguished, a crystalline-hexagonal packing characterized by a sharp 4.2Å diffraction band and a fluid (melted) state identified with a broad, diffuse band at 4.6Å.

At the growth temperature (30°C) the promitochondria of the anaerobic cells contain lipids which are predominantly in the gel state with ordered lipid chains, whereas the mitochondria of the aerobic cells are in the liquid crystalline or fluid state with "melted” chains.

A comparison of the phase transitions of intact membranes and extracted lipids suggests that lipid-protein interaction contributes to the high lipid phase transition temperature of promitochondria. Analysis of the spin probe data indicates a different organization of lipid and protein in such membranes, whilst the greater fluidity in the polar head group and in the lipid core of the differentiated mitochondria reflects the dynamic properties of the membrane lipids on the newly assembled proteins.

Discontinuities in the ATPase Arrhenius plots are observed: with the promitochondria the discontinuity occurs near the beginning of the lipid phase transition and the ATPase enzyme may be associated with the most mobile lipid regions within the membrane- With the fully organized mitochondria it occurs well above the phase transition.

A significant difference has been found in the magnetic resonance spectra from mitochondrial membranes and purified OS-ATPase. The spin label incorporated in the crude membrane is located in a more fluid region than label in an OS-ATPase system, supporting suggestion of the immobilization of lipid in the immediate vicinity of the protein. These results lend suggestion that fluid lipid regions not interacting with proteins could exist in the differentiated mitochondrial membranes and/or specific phospholipids could be involved as physiological regulators of ATPase activity by inducing a proper conformation in the enzymic activity.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QH Natural history Q Science > QK Botany Q Science > QP Physiology
Library of Congress Subject Headings (LCSH):	Membranes (Biology) -- Fluidity, Mitochondrial membranes, Saccharomyces cerevisiae, Lipoproteins
Official Date:	May 1975
Dates:	Date Event May 1975 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Griffiths, D. E.
Extent:	[10], 84 leaves : illustrations
Language:	eng

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