Biomedical subjects

A Ducret

Publications and source records attributed to A Ducret.

23 records · Page 2Linked to original sources

PubMed1996

Isolation, characterization and electron microscopy analysis of a hemidiscoidal phycobilisome type from the cyanobacterium Anabaena sp. PCC 7120.

In this work we present the characterization of a hemidiscoidal phycobilisome type of the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120. The phycobilisome of this organism contains allophycocyanin, phycocyanin and phycoerythrocyanin, similar to the closely related thermophilic cyanobacterium Mastigocladus laminosus. Intact phycobilisomes exhibit an absorption maximum at 619 nm and two fluorescence maxima at 664 nm and 680 nm, corroborating the presence of a complete energy pathyway along the antenna. Upon dissociation, the phycobiliproteins were released from the phycobilisome. One phycoerythrocyanin, one phycocyanin and three allophycocyanin complexes were isolated by ion-exchange chromatography and characterized by absorption and fluorescence spectroscopy and by SDS/PAGE. The amino-terminal sequences of the polypeptides belonging to the phycoerythrocyanin and phycocyanin families were identical with the derived sequences of their corresponding genes. Partial amino-terminal sequences of the polypeptides belonging to the allophycocyanin family are presented here. Our results show that the phycobiliproteins and linker polypeptides from Anabaena sp. PCC 7120 are similar to the phycobilisome components characterized in other cyanobacteria. The phycobilisome of Anabaena sp. PCC 7120 was extensively analyzed by electron microscopy. It differs from the common hemidiscoidal tricylindrical, six-rod phycobilisome type by a core domain consisting of five core cylinders surrounded by up to eight rods radiating in a hemidiscoidal manner. One rod is linked to each basal core cylinder, whereas the remaining core cylinders bind two rods each. On the basis of the data presented in this work, a revised model for the hemidiscoidal pentacylindrical phycobilisome of Anabaena sp. PCC 7120, M. laminosus and Anabaena variabilis is proposed. This model accounts more accurately for the 'grape' pattern typically exhibited by these phycobilisomes in electron micrographs.

Amino Acid Sequence↗

PubMed1996

Characterization of human serum amyloid A protein isoforms separated by two-dimensional electrophoresis by liquid chromatography/electrospray ionization tandem mass spectrometry.

A detailed structural analysis of the serum amyloid A proteins (SAA) of an individual with highly active, chronic rheumatoid arthritis is reported. SAA isoforms were separated by high-resolution two dimensional (2-D) gel electrophoresis. Peptide mapping by reverse-phase chromatography/electrospray ionization tandem mass spectrometry was applied to correlate the protein(s) contained in each spot with their respective coding gene and to study the post-translational processing and modification events which might result in differential electrophoretic mobility. Nine protein spots were analyzed. The six major spots corresponded to the Arg and des-Arg forms of SAA1 alpha and SAA2 alpha, respectively, and to the glycosylated and nonglycosylated form of constitutive serum amyloid A protein (C-SAA). Two minor spots were identified as SAA1 alpha isoforms containing post-translational modifications. We suggest that these variants contained a gamma-N, N'-dimethylasparagine residue at position 83 and that one of them was additionally oxidized at Trp53 and Trp85. The ninth spot was shown to contain a mixture of SAA1 alpha and SAA2 alpha. To our knowledge, this is the first report in which analysis of peptides has been used to verify the presence of C-SAA in acute-phase serum. Furthermore, the data illustrate that extensive post-translational processing results in a structurally diverse class of acute-phase SAA proteins, which are derived from a small number of genes. Finally, the fast and conclusive technology used in this study promises to be generally useful for the comprehensive investigation of proteins at the level of the primary structure.

Amino Acid Sequence↗

PubMed1996

Protein identification by solid phase microextraction-capillary zone electrophoresis-microelectrospray-tandem mass spectrometry.

We describe an analytical system for the rapid identification of proteins by correlation of tandem mass spectra with protein sequence databases. The system consists of an integrated solid phase microextraction/capillary zone electrophoresis peptide separation device that is connected through a microelectrospray ion source to a tandem mass spectrometer. The limits of detection are 660 amol of sample at a concentration limit of < 33 amol/microliters for peptide mass measurement, and < 10 fmol of sample, at a concentration limit of < 300 amol/microliters for peptide analysis by collision-induced dissociation. Using this system, we have identified low nanogram amounts of yeast proteins separated by high-resolution two-dimensional gel electrophoresis.

Databases, Factual↗

PubMed1994

The complete amino acid sequence of R-phycocyanin-I alpha and beta subunits from the red alga Porphyridium cruentum. Structural and phylogenetic relationships of the phycocyanins within the phycobiliprotein families.

We present here the complete primary structure of R-phycocyanin-I alpha and beta subunits from the red alga Porphyridium cruentum. The alpha chain is composed of 162 amino acid residues (18049 Da, calculated from sequence, including chromophore) and carries a phycocyanobilin pigment covalently linked to Cys84. The beta chain contains 172 amino acids (19344Da, calculated from sequence, including chromophores) and carries a phycocyanobilin pigment covalently linked at Cys82 and a phycoerythrobilin pigment at Cys153. A gamma-N-methyl asparagine residue was also characterised at position beta 72 similar to other phycobiliprotein beta subunits. R-phycocyanin-I from Porphyridium cruentum shares high sequence identity with C-phycocyanins (69-83%), R-phycocyanins (66-70%) and in a less extent with phycoerythrocyanins (57-65%) from various sources. The presented phylogenetic trees are based on a comparison of all phycobiliprotein amino acid sequences known so far and confirm the clear affiliation of the R-phycocyanins in the phycocyanin family. In spite of their particular phycobilin pattern, they do not represent intermediate forms between the phycocyanin and the phycoerythrin family. Phycoerythrocyanin, a phycocyanin-related phycobiliprotein adapted to green light harvesting, is also shown to belong to the phycocyanin family. However, the phycoerythrocyanins diverge from phycocyanins in their different function and it is suggested that they should be assigned to a separate group within the phycocyanin family.

Amino Acid Sequence↗

PubMed1987

Technetium 99m labelled heparin: pharmacokinetics and tissue distribution in rats after vascular surgery.

Pharmacokinetics of technetium 99m (99mTc) labelled heparin was studied after I.V. infusion (70 IU/kg) in normal rats and in a group of animals just after aortic longitudinal incision and suture. Anticoagulant activity measurements and radioactivity were compared on the same plasma samples. The pharmacokinetic decay of 99mTc-heparin followed a bi-exponential pattern. Half-lives (T1, T2) were significantly shortened after surgery using both techniques. Liver accumulation of labelled heparin was decreased in "sutured" rats and a high uptake of 99mTc-heparin was found on the operated area of the aorta.

Animals↗