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Time-Resolved X-Ray Diffraction Studies on Biological Systems

100%

Rapp G.

Acta Physica Polonica A

1992

vol. 82

issue 1

103-120

Understanding of biological function requires knowledge both on structural and dynamical aspects. The aim of time-resolved X-ray diffraction is to combine structural and kinetic methods by monitoring structural or conformational changes within a single protein or assemblies of proteins during their biological action in real time. This requires (i) a powerful X-ray source, (ii) appropriate detectors capable of dealing with high local and total count rates and (iii) a suitable trigger mechanism. These aspects are briefly discussed with emphasis on light as trigger for initiation of structural or conformational changes. Examples are presented on muscle contraction, lipid phase transitions, the photocycle of bacteriorhodopsin and the application of Laue crystallography on the protein p21.

X-Ray Diffraction and NMR Studies on Mixtures of Non-Ionic Surfactant (C_{12}EO_{2}) and Phospholipids (POPC)

51%

Funari S. S., di Vitta C., Rapp G.

Acta Physica Polonica A

1997

vol. 91

issue 5

953-960

We studied the temperature and concentration dependence of the POPC/C_{12}EO_{2}/water ternary system and identified and characterized the different phases occurring. The thermal behaviour is slightly dependent on the surfactant to lipid molar ratio R_{s/l}. At low surfactant content the behaviour is similar to the binary lipid/water system. Similarly at low lipid contents the system behaves similarly to the surfactant/water mixture. However, at molar ratios R_{s/l} between 2 and 3 a new hexagonal phase forms which is peculiar to the mixture. ^{2}H NMR measurements indicated the existence of a lamellar phase containing also curved surfaces additional to the flat ones. The surface area per surfactant molecule was calculated to 0.23 nm^{2} which is in good agreement with the cross-section of a paraffinic chain.

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2 Acta Physica Polonica A

1 1997

1 1992

2 Rapp G.

1 Funari S. S.

1 di Vitta C.

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Time-Resolved X-Ray Diffraction Studies on Biological Systems

X-Ray Diffraction and NMR Studies on Mixtures of Non-Ionic Surfactant (C_{12}EO_{2}) and Phospholipids (POPC)