Phase behaviour of the membrane lipids of the thermophilic blue-green alga Anacystis nidulans |
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| Affiliation: | 1. Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 8th St, Troy, New York 12180-3590, USA;2. Molecular Structure and Function, The Hospital for Sick Children, 686 Bay Street, Toronto, Ontario M5G 0A4, Canada;3. Department of Biochemistry, University of Toronto, 101 College Street, Toronto, Ontario M5G 1L7, Canada;1. Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil;2. Dipartimento di Chimica, Università di Pavia, Pavia, Italy;3. Centro de Ciências Exatas/Departamento de Química, Universidade Federal do Espírito Santo, Vitória, ES, Brazil;4. Central Analítica, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil;5. NEQC - Núcleo de Estudos em Química Computacional, Departamento de Química, ICE, Universidade Federal de Juiz de Fora, MG, Brazil |
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| Abstract: | The phase behaviour of total membrane lipid extracts of the blue-green alga Anacystis nidulans is compared with that of the individual lipid classes present in such extracts using fluorescence probe, differential scanning calorimetry, wide-angle X-ray diffraction and freeze-fracture techniques. Marked differences are observed in the properties of the isolated lipids as compared to the total lipid extracts. In particular, purified samples of monogalactosyldiacylglycerol and phosphatidylglycerol form complex high melting-point gel phases on storage which are not found in the membrane extracts. Addition of Mg2+ ions to the extracts is also shown to lead to an extensive phase separation of monogalactosyldiacylglycerol from the extracts. The enthalpy changes associated with phase separations occurring in the lipid extracts are found to be approx. 30% higher than those for the corresponding membranes, suggesting that the presence of other components, such as membrane proteins, may influence the phase behaviour of the lipids. The significance of these observations is discussed in terms of the factors limiting the stability of membrane systems. |
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