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D Oesterhelt

Publications and source records attributed to D Oesterhelt.

245 records · Page 14Linked to original sources
PubMed1973

Functions of a new photoreceptor membrane.

The purple membrane of Halobacterium halobium contains only one protein, bacteriorhodopsin, which closely resembles the visual pigments of animals. Light flashes cause a rapid transient shift of its absorption maximum from 560 to 415 nm. This shift is accompanied by release and uptake of protons. Respiring cells acidify the medium in the dark; if they contain purple membrane their O(2) consumption is reduced in the light. Starved or anaerobic cells containing purple membrane, in the absence of any apparent source of energy, generate and maintain a proton gradient across the cell membrane as long as they are exposed to light. We postulate that the light-generated proton gradient arises from a vectorial release and uptake of protons by bacteriorhodopsin, which is suitably oriented in the cell membrane and under continuous illumination oscillates rapidly between the long- and short-wavelength form. Preliminary results indicate that the gradient in H. halobium plays the central role in energy coupling attributed to such electrochemical gradients by Mitchell's chemiosmotic theory.

Aerobiosis↗
PubMed1969

Crystallization of a multienzyme complex: fatty acid synthetase from yeast.

The crystallization of purified fatty acid synthetase from yeast is facilitated by seeding techniques. The first seed crystals appeared as particles with almost negligible enzymatic activity in a solution that had been left at 4 degrees C for 15 months. Subsequently, the crystallization time has been reduced to two days, and the crystals now isolated have retained their full enzymatic activity. The loss of synthetase activity that can result from prolonged exposure during crystallization is attributable specifically to damage of the enzyme component responsible for condensation activity. Crystalline synthetase is identical to purified but noncrystalline synthetase by all criteria so far examined.

Crystallization↗
PubMedDate not supplied

Bacteriorhodopsin mutants D85N, D85T and D85,96N as proton pumps.

Proton translocation in the BR mutants D85N, D85T and D85,96N was studied by attachment of purple membranes to planar lipid bilayers. Pump currents in these mutants were measured via capacitive coupling and by use of the appropriate ionophores. All mutants have a reduced pK of their Schiff bases around 8-8.5 in common. At physiological pH, a mixture of chromophores absorbing at 410 nm (deprotonated form) and around 600 nm (protonated form) coexists. Excitation with continuous blue light induces in all three mutants an outwardly directed stationary pump current. These currents are enhanced upon addition of azide in D85N and D85,96N by a factor of 50, but no azide enhancement is observed in D85T. Yellow light alone induces transient inwardly directed currents in the mutants but additional blue light leads to a stationary current with the same direction. All the observed currents are carried by protons, so that the consecutive absorption of a yellow and a blue photon leads to inverted stationary photocurrents by the mutants, as observed with halorhodopsin (HR). A mechanistic model describing the inversion of proton pumping is discussed by the cis-trans, trans-cis isomerization of the retinal and the different proton accessibility of the Schiff base from the extracellular or the cytoplasmic side of the membrane.

Journal Article↗
PubMedDate not supplied

Phototrophic growth of halobacteria and its use for isolation of photosynthetically-deficient mutants.

Phototrophic growth conditions for halobacteria in complex and synthetic media have been established, demonstrating the photosynthetic capacity of this class of archaebacteria. Mutagenesis, 5-bromo-2'-deoxyuridine selection and screening techniques are described which are useful tools in the elucidation of the structure-function relationship of retinal proteins in halobacteria.

Anaerobiosis↗