Energy transfer processes in Gloeobacter violaceus PCC 7421 that possesses phycobilisomes with a unique morphology

We examined energy transfer dynamics in phycobilisomes (PBSs) of cyanobacteria in relation to the morphology and pigment compositions of PBSs. We used Gloeobacter violaceus PCC 7421 and measured time-resolved fluorescence spectra in three types of samples, i.e., intact cells, PBSs, and rod assemblies separated from cores. Fremyella diplosiphon, a cyanobacterial species well known for its complementary chromatic adaptation, was used for comparison after growing under red or green light. Spectral data were analyzed by the fluorescence decay-associated spectra with components common in lifetimes with a time resolution of 3 ps/channel and a spectral resolution of 2 nm/channel. This ensured a higher resolution of the energy transfer kinetics than those obtained by global analysis with fewer sampling intervals. We resolved four spectral components in phycoerythrin (PE), three in phycocyanin (PC), two in allophycocyanin, and two in photosystem II. The bundle-like PBSs of G. violaceus showed multiple energy transfer pathways; fast ( approximately 10 ps) and slow ( approximately 100 ps and approximately 500 ps) pathways were found in rods consisting of PE and PC. Energy transfer time from PE to PC was two times slower in G. violaceus than in F. diplosiphon grown under green light.     

Two unique cyanobacteria lead to a traceable approach of the first appearance of oxygenic photosynthesis

The evolutionary route from anoxygenic photosynthetic bacteria to oxygenic cyanobacteria is discontinuous in terms of photochemical/photophysical reaction systems. It is difficult to describe this transition process simply because there are no recognized intermediary organisms between the two bacterial groups. Gloeobacter violaceus PCC 7421 might be a model organism that is suitable for analysis because it still possesses primordial characteristics such as the absence of thylakoid membranes. Whole genome analysis and biochemical and biophysical surveys of G. violaceus have favored the hypothesis that it is an intermediary organism. On the other hand, species differentiation is an evolutionary process that could be driven by changes in a small number of genes, and this process might give fair information more in details by monitoring of those genes. Comparative studies of genes, including those in Acaryochloris marina MBIC 11017, have provided information relevant to species differentiation; in particular, the acquisition of a new pigment, chlorophyll d, and changes in amino acid sequences have been informative. Here, based on experimental evidence from these two species, we discuss some of the evolutionary pathways for the appearance and differentiation of cyanobacteria.     

Magnetic circular dichroism properties of reaction center complexes isolated from the zinc-bacteriochlorophyll a-containing purple bacterium Acidiphilium rubrum

Reaction center (RC) complexes isolated from a Zn-bacteriochlorophyll (BChl) a-containing purple bacterium, Acidiphilium rubrum, were characterized by absorption, circular dichroism, and magnetic circular dichroism (MCD) spectroscopy. The oxidized-minus-reduced difference spectra indicated that, in this RC, the Zn-BChl a is the primary electron donor. The molecular structure of the donor was examined by measuring the ratio of the MCD intensity of the Faraday B-term (B) to the dipole strength (D). In the Q(y) region, B/D for the donor was about half those of bacteriopheophytin a and the accessory Zn-BChl a, indicating that the primary electron donor is a dimer. The magnitude of bleach of the Q(x) band was half that observed in Rhodobacter sphaeroides, suggesting the cation is localized on a single Zn-Bchl a. The absorption intensity of the higher-energy Q(y) exciton band was approximately 28% of that of the lower-energy band, and the exciton splitting was approximately 570 cm(-1), smaller than that in Rb. sphaeroides. These results indicate that, in A. rubrum, the primary electron donor is a Zn-BChl a dimer but that the interaction between the two molecules is rather weak. On the basis of these results, an adaptive strategy for changes in BChl a species is discussed from an evolutionary perspective.     

Quest for minor but key chlorophyll molecules in photosynthetic reaction centers – unusual pigment composition in the reaction centers of the chlorophyll d-dominated cyanobacterium Acaryochloris marina

A short overview, based on our own findings, is given of the minor pigments that function as key components in photosynthesis. Recently, we found the presence of chlorophyll a, chlorophyll d′ and pheophytin a as minor pigments in the chlorophyll d-dominated cyanobacterium Acaryochloris marina. This revised version was published online in June 2006 with corrections to the Cover Date.     

N-terminus conservation in the terminal pigment of phycobilisomes from a prokaryotic and eukaryotic alga

High molecular weight polypeptides from phycobilisomes, believed to be involved in facilitating the energy flow from phycobilisomes to thylakoids, are conserved in the prokaryote Nostoc sp. and the eukaryote Porphyridium cruentum. Partial N-terminal sequence analysis of the phycobilisome-polypeptides of Nostoc (94 kilodalton) and Porphyridium (92 kilodalton) revealed 55% identity in the first 20 residues, but no significant homology with sequences of other phycobiliproteins or phycobilisome-linkers. Polypeptides (94 and 92 kilodalton) from Nostoc thylakoids free of phycobilisomes, previously presumed to be involved in the phycobilisome-thylakoid linkage (M Mimuro, CA Lipschultz, E Gantt 1986 Biochim Biophys Acta 852: 126) exhibit the same immunocrossreactivity but are different from the 94 kilodalton-phycobilisome polypeptide by having blocked N-termini and a different amino acid composition.     

Purification of a protein from bovine plasma that binds to type 1 plasminogen activator inhibitor and prevents its interaction with extracellular matrix. Evidence that the protein is vitronectin

Type 1 plasminogen activator inhibitor (PAI-1) binds to the extracellular matrix of cultured bovine aortic endothelial cells. Bovine plasma and bovine lung extract contain protein(s) that bind to PAI-1 and prevent this interaction. One of these proteins was purified approximately 425-fold from ammonium sulfate-fractionated plasma using standard chromatographic procedures together with affinity chromatography on PAI-1-Sepharose. The final product consisted of a major polypeptide of Mr 65,000 and two minor polypeptides of Mr 80,000 and 57,000. NH2-terminal amino acid sequence analysis of the Mr 65,000 polypeptide revealed that it was homologous with vitronectin, and antiserum against this purified binding protein recognized vitronectin and vice versa. Immunological analysis using these antisera demonstrated that the three peptides were immunologically related, and that vitronectin was present in the extracellular matrix of bovine endothelial cells and also in bovine lung.     

Fibrinolytic components in nasal mucosa and nasal secretion

 We evaluated a possible role for fibrinolytic components in nasal secretion by tissue localization with immunohistochemical techniques and by measuring their antigen concentrations in nasal discharge by means of ELISA and fibrin autography. Nasal mucosa was obtained surgically from the inferior turbinate. Urokinase-type plasminogen activator (u-PA) specific staining was observed in pseudostratified ciliated epithelium and was predominant in mucous cells of the seromucinous gland, while serous cells were almost devoid of stain. The pattern of staining of plasminogen activator inhibitor-2 was similar to that of u-PA. In contrast, plasminogen activator inhibitor-1(PAI-1) immunoreactive material was localized exclusively in serous cells of seromucinous glands. Positive staining for tissue-type plasminogen activator (t-PA) was observed in endothelial cells and basal cells, which differentiate into either ciliated or goblet cells. Nasal secretions were partially fractionated by immunospecific antibody-immobilized Sepharose. Subsequent fibrin autography patterns indicated the presence of u-PA, PAI-1, and t-PA. After methacholine provocation, the level of t-PA increased transiently but decreased rapidly with subsequent challenges. These differential stainings of fibrinolytic components and the existence of PAs and PAI-1 in the nasal discharge suggest that the fibrinolytic system may play a role in the movement and fluidity of nasal secretion. Accepted: 25 May 1998     

Crystallization and preliminary X-ray diffraction studies of C-phycocyanin from a red alga, Porphyra tenera

C-Phycocyanin from a red alga, Porphyra tenera, has been crystallized by the vapor-diffusion procedure. Both orthorhombic and hexagonal forms were obtained from ammonium sulfate solutions, whereas only the orthohombic form was selectively grown from sodium citrate solutions. The orthorhombic crystals are more suitable for further crystallographic work; their space group is P2(1)2(1)2(1), with unit-cell dimensions of a = 105, b = 121, and c = 184 A. The asymmetric unit comprises two (alpha beta)3 trimer molecules of C-phycocyanin. These crystals diffract X-rays up to about 3 A resolution.