Biomedical subjects

M Picaud

Publications and source records attributed to M Picaud.

17 recordsLinked to original sources

PubMed1990

Towards the understanding of the function of Rb sphaeroides Y wild type reaction center: gene cloning, protein and detergent structures in the three-dimensional crystals.

We report various experiments aimed at the resolution of the 3-dimensional structure of the photosynthetic reaction center from wild type Y Rhodobacter sphaeroides. The genes encoding the L and M polypeptides have been cloned and sequenced. They bear 2 mutations each when compared to those already sequenced in another Rb sphaeroides strain (2.4.1). In the L gene, these codon changes are silent. In the M gene, one is silent and the other one leads to a Leu-Met substitution at position 140. At the present stage of the refinement of the X-ray data (0.3 nm resolution) the structure of the Y reaction center is shown to be highly similar to that of the Rhodopseudomonas viridis reaction center. The binding of spheroidene on the M side of the Y reaction center is shown to be determined by hydrophobic interactions with neighboring amino acids and by steric factors. Preliminary results concerning the localization of the detergent (beta-octylglucoside) in the unit cell are presented. This method combines low angle neutron scattering at different contrasts in H2O/D2O with X-ray crystallographic data.

Carotenoids↗

PubMed1989

Mutations responsible for high light sensitivity in an atrazine-resistant mutant of Synechocystis 6714.

The primary target of photoinhibition is the photosystem II reaction center. The process involves a reversible damage, followed by an irreversible inhibition of photosystem II activity. During cell exposition to high light intensity, the D1 protein is specially degraded. An atrazine-resistant mutant of Synechocystis 6714, AzV, reaches the irreversible step of photoinhibition faster than wild-type cells. Two point mutations present in the psbA gene of AzV (coding for D1) lead to the modification of Phe 211 to Ser and Ala 251 to Val in D1. Transformation of wild-type cells with the AzV psbA gene shows that these two mutations are sufficient to induce a faster photodamage of PSII. Other DCMU- and/or atrazine-resistant mutants do not differ from the wild type when photoinhibited. We conclude that the QB pocket is involved in PSII photodamage and we propose that the mutation of Ala 251 might be related to a lower rate of proteolysis of the D1 protein than in the wild type.

Amino Acid Sequence↗

PubMed1989

Molecular analysis of psbA mutations responsible for various herbicide resistance phenotypes in Synechocystis 6714.

Mutations conferring herbicide resistance in 3 mutant strains of the cyanobacterium Synechocystis 6714 have been characterized by gene cloning and sequencing. The mutants display very different phenotypes: DCMU-IIA is DCMU-resistant and atrazine-resistant, DCMU-IIB is DCMU-resistant and atrazine-sensitive, and Az-V is DCMU-sensitive, atrazine-resistant and presents particular photoinhibition properties. These mutants were originally obtained either by one-step selection (DCMU-IIA) or by two-step selection (DCMU-IIB and Az-V). psbA copies carrying herbicide resistance have been identified by transformation experiments as psb AI in all cases. Sequences of the psb AI copy of each mutant have been compared to the wild-type sequence. In the single mutant DCMU-IIA, a point mutation at codon 264 (Ser----Ala) results in resistance to both DCMU and atrazine. In the double mutants DCMU-IIB and Az-V, two point mutations were found. DCMU-IIB was derived from DCMU-IIA and had acquired a second mutation at codon 255 (Phe----Leu) resulting in a slight increase in DCMU resistance and complete abolition of atrazine resistance. Az-V contains two changes at codons 211 (Phe----Ser) and 251 (Ala----Val) resulting in high atrazine resistance but only slight DCMU resistance.

Amino Acid Sequence↗

PubMed1980

Chlorophyll fluorescence as a probe for the determination of the photo-induced proton gradient in isolated chloroplasts.

Gramicidin D-treated chloroplasts show an acid-induced quenching of the chlorophyll fluorescence, which is composed of a reversible and irreversible part. The reversible quenching is analogous to the photo-induced quenching in coupled chloroplasts and can be taken to determine the light induced delta pH.

Chlorophyll↗

PubMed1979

A quantitative study of the slow decline of chlorophyll a fluorescence in isolated chloroplasts.

A detailed study of the photo-induced decline in chlorophyll a fluorescence intensity (Kautsky phenomenon) in coupled isolated chloroplasts from a high level (P) to a low stationary level (S) is presented. 1. A linear relationship between P leads to S quenching and intrathylakoid H+ concentration was found. When the light-induced proton gradient was abolished by uncoupling, the fluorescence emission at room temperature was lowered proportionally to increased H+ concentration in the medium. 2. Fluorescence spectra at -196 degrees C of samples frozen at the P and S states showed no significant differences in the Photosystem I/Photosystem II ratio of fluorescence emission. Furthermore, freezing to -196 degrees C reversed the P leads to S quenching. This indicates that the P leads to S quenching is not related to an increase of spillover of excitation energy from Photosystem II to Photosystem I. 3. When Mg2+ was added to thylakoids suspended in a medium free of divalent cations, the inhibition of spillover required lower Mg2+ concentrations (half saturation at 0.6 mM). Increased proton concentration in the medium also inhibited spillover. 4. The results are interpreted in terms of two sites of Mg2+ and H+ effects on excitation deactivation in Photosystem II. One site is located on the outer face of the thylakoid membrane; action of both Mg2+ and H+ at this side diminishes spillover. The second site is located on the inner face of the membrane; as Mg2+ is displaced there by protons, a non-photochemical quenching of Photosystem II fluorescence is induced, which is manifested by the P leads to S decline.

Chlorophyll↗

PubMed1979