Oral Session
S2 Structure and Function of Proteins
January 19, Monday
Morning session (09:00〜11:55)
S2-O1〜S2-O9
Chairperson:
Prof. W. N. KONINGS
Prof. N. J. RUSSELL
Afternoon session (14:45〜17:50)
S2-O10〜S2-O18
Chairperson:
Prof. J. G. ZEIKUS
Prof. B. E. JONES
Jack L.C.M. VAN DE VOSSENBERG, Arnold J.M. DRIESSEN, and Wil N. KONINGS*
Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
Energy transduction processes in the cell membranes of bacteria and archaea can only occur efficiently when the membranes are limited permeable for the cations which are used in energy-coupling. This can be protons, sodium-ions or both. The proton and sodium-ion permeability was measured in unilaminar liposomes of uniform size, prepared from the lipids extracted from bacteria and archaea grown at a wide range of growth temperatures (1). In all liposomes the rate constant of the proton permeability and of the sodium-ion permeability increased with the temperature. The temperature dependency of the sodium-ion permeability rate constant was the same for all liposomes irrespective of where the lipids were isolated from. The temperature dependency of the rate constant of the proton permeability, however, varied drastically with the origin of the lipids. Liposomes prepared from cryophilic bacteria became already very permeable at low temperatures, while liposomes prepared from mesophilic bacteria and archaea became permeable at mesophilic temperatures. The surprising observation was made that the proton permeability of all liposomes prepared from the cryophilic bacteria and the mesophilic bacteria and archaea had the same rate constant of proton permeability at the growth temperature at which the organisms were grown. This also holds for the liposomes constructed from the tetra-ether lipids from thermophilic archaea. In contrast, the liposomes prepared from the lipids of thermophilic bacteria were already very permeable for protons at much lower temperatures than the growth temperature.
These observations suggested: (i) bacteria and archaea, with the exception of thermophilic bacteria, can adjust the lipid composition of the membrane in such a way that the proton-permeability remains within a narrow range; (ii) for thermophilic bacteria sodium-ions are more suitable coupling ions than protons. Both suggestions were confirmed in subsequent studies. To test the first suggestion Bacillus subtilis was grown at the lowest and highest temperature at which growth still occurred at a reasonable rate (2). These temperatures were 13℃ and 50℃, respectively. The head group composition of the cytoplasmic membrane lipids derived from these cells did not differ significantly, but the averaged lipid acyl chain length, degree of saturation, and ratio of iso- and ante-iso branched fatty acids increased with the temperature. Fluidity measurements revealed that at both temperatures the membrane is in the fluid- crystalline state, but at 13℃ the membrane is four fold more viscous than at 50℃. These observations show that homeo-viscous adaptation determines to a limiting
