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D Oesterhelt

Publications and source records attributed to D Oesterhelt.

At least 217 records · Page 12Linked to original sources
PubMed1980

Orthorhombic two-dimensional crystal form of purple membrane.

A new two-dimensional crystal form of purple membrane has been obtained in vitro. It is produced by the joint use of a cationic detergent, dodecyltrimethylammonium chloride, and the nonionic detergent, Triton X-100. It primarily forms large, rolled-up sheets that look like needles in the light microscope. Liposomes and tubes are also observed. The absorption maximum of the new form of purple membrane is blue-shifted by 6 nm and its density is slightly lower than the natural form of purple membrane. The new form of purple membrane is orthorhombic with space group p22121 and cell dimensions 57.6 x 73.5 A. Four molecules of bacteriorhodopsin occupy the unit cell with an area per molecule close to that found in the native p3 structure. The projected structure to 6.5-A resolution was determined by electron microscopy and diffraction. It shows an identical molecular structure to that of the p3 form and determines the position of the polypeptide boundary.

Bacteriorhodopsins↗
PubMed1980

Three-dimensional crystals of membrane proteins: bacteriorhodopsin.

The intrinsic membrane protein bacteriorhodopsin has been crystallized by salt precipitation after solubilization by octyl glucoside. Two different crystal forms were obtained, depending on the nature of the salt used and the pH. Needles formed in the presence of sodium phosphate and in ammonium sulfate solutions above pH 4.8. Cubes appeared in sodium citrate solutions or ammonium sulfate. Unlike the cubic crystals, the birefringent needles showed strong linear dichroism, which allowed determination of the orientation of the chromophore's transition moment. The procedure described here may be of general use in crystallographic studies of membrane proteins.

Bacteriorhodopsins↗
PubMed1980

Anaerobic growth of halobacteria.

An energy-transducing pathway in halobacteria is described. Arginine mediates substrate level phosphorylation and allows the cells to grow anaerobically. Bacteriorhodopsin plus light can function as an alternative energy source under these conditions, provided the cells contain the pigment when transferred to the anaerobic environment. Therefore the selection of mutants functionally defective in ATP synthase or bacteriorhodopsin becomes possible.

Adenosine Triphosphate↗
PubMed1979

Chromophore equilibria in bacteriorhodopsin.

An investigation of the dark equilibria between different chromophores of bacteriorhodopsin (BR) and studies of the kinetics of their interconversion and photochemical activity have led to the following conclusions. (a) A component of the 605-nm chromophore of BR decays in the millisecond range and is likely to be identical to the intermediate O of the photochemical cycle of BR and is assumed to be formed from the purple complex (PC) by the binding of one proton to BR. (b) An acidic form the PC, PCaL-, arises from the 605-nm chromophore by selective binding of anions L- (F- greater than Cl- greater than Br- greater than I- greater than Cl04-) to BR. (c) The isomeric equilibrium between 13-cis and all-trans retinal is approximately 0.15/0.85 in PCaCl-, 0.3/0.7 in the 605-nm chromophore as compared to 0.5/0.5 in the PC. (d) The 500-nm chromophore is formed from the PC by release of nearly one proton from BR. (e) The pH range in which the PC exists is reduced in a high-temperature structure of the purple membrane as compared to its low temperature structure. A model for the chromophore structure is proposed as a hypothesis, which allows a comprehensive interpretation of the results. In this model the absorption spectrum of the retinylidene lysine Schiff base is modulated by its protonation state and the interaction with an anionic group.

Anions↗
PubMed1978

Specificity of the retinal binding site of bacteriorhodopsin: chemical and stereochemical requirements for the binding of retinol and retinal.

The complexes formed from bacteriopsin and various retinyl compounds were analyzed by fluorescence and absorption spectroscopy. The binding of retinol occurs in two steps. In the first reaction the molecule is fixed in the retinal binding site of the protein. In this state, energy transfer from aromatic amino acid residues to the retinyl moiety is observed. all-trans-Retinal and the 13-, 11-, and 9-cis-retinols are bound in the chromophoric site. In the second reaction the cyclohexene ring and the side chain of the retinyl moiety are forced into a planar conformation. This reaction is mediated by a base (B1) with a pK of 3.8 and requires the oxygen atom but not the free hydroxyl group of retinol, indicating interaction with a group AH (pK greater than or equal to 10.5). The ring-chain planarization reaction is blocked for the 9-cis isomer of retinol. Binding studies with bacterioopsin and retinal isomers reveal that, as in the case of the corresponding retinols, B1 mediates ring-chain planarization in the case of the all-trans, 13-cis, and 11-cis isomers but not with the 9-cis isomer. Reconstitution of the purple complex from the intermediate 430-460-nm chromophore requires the presence of a second base (B2) with a pK of 4.6. This reaction is exclusive for all-trans- and 13-cis-retinal

Bacteriorhodopsins↗
PubMed1978

Potassium uniport and ATP synthesis in Halobacterium halobium.

Light-driven potassium ion uptake in Halobacterium halobium is mediated by bacteriorhodopsin. This uptake is charge-balanced by sodium ions and not by proton release. Light-induced shifts in concentrations of divalent cations were found to be negligible. The transient changes in extracellular pH (alkaline overshoot) can be understood by the concomitant processes of ATP synthesis, proton/sodium exchange and potassium uptake. The driving force of potassium ion uptake is the membrane potential, no ATP-dependent potassium transport process is found. Fluorescence measurements indicate a high permeability of the membrane to potassium ions compared to sodium ions. Therefore the potassium ion diffusion potential contributes to the membrane potential (about 30 mV/decade) and thereby influences the ATP level. Sudden enhancement of the diffusion potential by the potassium ionophore monactin leads to the expected transient increase in cellular ATP level. Due to the large size (up to 100-fold) of the potassium ion gradient and its high capacity (intracellular concentration up to 3 M) the potassium ion gradient can well serve the cell as a long term storage form of energy.

Adenosine Diphosphate↗
PubMed1978

Complete amino acid sequence of Halobacterium halobium ferredoxin containing an Nepsilon-acetyllysine residue.

1. The complete amino acid sequence of the 2Fe-2S ferredoxin from Halobacterium halobium was determined to be: (formula see text):2. The apoferredoxin chain consists of 128 amino acid residues and has a molecular weight of 14,330. 3. There are only four cysteines in this ferredoxin molecule; they should be involved in the binding of the two iron atoms at the active center. Ther relative positions of these cysteines are similar to those of the cysteines in chloroplast ferredoxins. 4. There is a high degree of homology between H. halobium ferredoxin and chloroplast ferredoxins, though the latter molecules contain only about 98 amino acid residues. 5. H. halobium ferredoxin contains a single residue of Nepsilon-acetyllysine.

Amino Acid Sequence↗
PubMed1977

Reaction of yeast fatty acid synthetase with iodoacetamide. 3. Malonyl-coenzyme A decarboxylase as product of the reaction of fatty acid synthetase with iodoacetamide.

Yeast fatty acid synthetase possesses very low malonyl-CoA decarboxylase activity. Treatment with iodoacetamide, while abolishing synthetase activity, induces a strong malonyl decarboxylase activity which, in turn, can be inhibited by N-ethylmaleimide. Kinetic analysis shows that the emergence of the decarboxylase activity is synchronized to the disappearance of the fatty-acid-synthesizing activity and thus, is due to carboxamidomethylation of the peripheral SH-groups of the multienzyme complex. Strong decarboxylase activity was also found after treatment of the synthetase with methylmalonyl-CoA. A hypothetical scheme is proposed which explains the origination of the decarboxylase activity as a consequence of conformational changes of the condensing enzyme component which happen when the peripheral SH-group is acylated or alkylated.

Binding Sites↗
PubMed1977

Bacteriorhodopsin-mediated photophosphorylation in Halobacterium halobium.

The rate of halobacterial photophosphorylation was found to be a linear function of light intensity over a wide range (between 1 and 20 mW/cm2). At higher light intensities (above 25 mW/cm2) the ATP-synthesizing system itself limits the maximal rate of photophosphorylation. The optimal external pH range for this type of photophosphorylation is between pH 6.2 and 7.2 external. The photophosphorylation rate is directly proportional to the bacteriorhodopsin content of the cells. The quantum requirement for photophosphorylation was found to be 22 +/- 5 photons per ATP molecule synthesized. According to Mitchell's chemiosmotic hypothesis of energy coupling phosphorylation can be driven by a membrane potential or a pH gradient or a combination of both. From the results of experiments with drugs which abolish or reduce either one of the two components we conclude that the major driving force for photophosphorylation above an external pH value of 6.5 is the membrane potential, while at more acidic pH value the pH gradient becomes dominating. We did not observe a correlation between a transient alkalinization of the medium and ATP-synthesis upon illumination under certain conditions.

Adenosine Triphosphate↗
PubMed1977

Direction of proton translocation in proteoliposomes formed from purple membrane and acidic lipids depends on the pH during reconstitution.

The reconstitution of proton pumping activity in proteoliposomes formed by brief sonication of purple membrane and lipid dispersions was studied as a function of pH. Proteoliposomes reconstituted using cardiolipin showed light-dependent proton extrusion when formed at a pH below 2.75 and proton uptake when formed above pH 2.75. Several other acidic lipids including halobacterial lipids behaved similarly. The experiments suggest that the degree of dissociation of the lipid phosphate groups determines the preferential orientation of bacteriorhodopsin in reconstituted proteoliposomes.

Bacteriorhodopsins↗