Biliprotein assembly in the hemidiscoidal phycobilisomes of the thermophilic cyanobacterium Mastigocladus laminosus Cohn. Characterization of dissociation products with special reference to the peripheral phycoerythrocyanin-phycocyanin complexes

The dissociation products of isolated phycobilisomes of Mastigocladus laminosus were separated and analyzed by ultracentrifugation and, in part, by isoelectric focusing. With the exception of the allophycocyanin core, the sedimentation constants of peripheral phycocyanin- and phycoerythrocyanin-phycocyanin complexes lay in the range of 6 to 17S. The latter was represented by a 17S aggregate of two hexameric phycocyanins (dodecamer, dipartite unit). A complex with an absorption maximum at 610 nm (phycocyanin) and a shoulder at 580 nm (phycoerythrocyanin), a fluorescence emission maximum at 645 nm and a sedimentation constant of 11 S is described as a heterogeneously composed hexamer of ()₃-phycoerythrocyanin-()₃-phycocyanin. It was stable under extended dissociation in the cold and under isoelectric focusing. An aggregate of 14 S with an absorption maximum at 576 nm and a shoulder in the fluorescence emission spectrum at 625 nm (phycoerythrocyanin) in addition to the maximum at 645 nm (phycocyanin) is interpreted as a polar phycoerythrocyanin/ phycoerythrocyanin-phycocyanin complex. Combining these complexes with phycocyanin dodecamers creates peripheral rods of the phycobilisome. A proposal of the phycobiliprotein distribution within the phycobilisome of M. laminosus is presented.Abbreviations APC allophycocyanin - PC phycocyanin - PE phycoerythrin - PEC phycoerythrocyanin     

RexAB proteins of bacteriophage lambda enhance the effect of photolyase-dimer complexes on lacZ gene expression in Escherichia coli.

Summary Expression of the lacZ gene in Escherichia coli is inactivated by exposure to ultraviolet light (UV). Inactivation is exceptionally effective when cells contain amplified levels of DNA photolyase (which forms complexes with pyrimidine dimers in the absence of light for actual photoreversal) and a prophage. Without amplified photolyase, the prophage or both, inactivation rates are similar and much lower. UV-inactivation of lacZ gene expression in the presence of both amplified photolyase and is even more effective if cI857 is used in place of the wildtype prophage but is wholly unexceptional if the prophage carries defects in the genes rexA or rexB. When Rex AB proteins are provided by expression from a plasmid and the cell also contains amplified photolyase, exceptional inactivation rates again obtain; in fact inactivation is most effective under these conditions. The data are considered to reveal a role for Rex AB proteins, which mediate superinfection exclusion, in the exceptional inactivation of gene expression by photolyase bound to pyrimidine dimers in DNA. Photolyase-dimer complexes may mimic the structure of certain complexes that arise during phage development and thus influence Rex A and/or B proteins, thereby shutting down cell metabolism.     

Freeze fracture immunocytochemistry of light-harvesting pigment complexes in a cryptophyte

Summary Immunocytochemical techniques using colloidal gold as the marker have been used to examine the location of the two light harvesting pigment-protein complexes in cryptophyte chloroplasts. A comparison of post-embedding thin section labelling and freeze fracture labelling has been carried out onRhodomonas salina using polyclonal antibodies to a chlorophylla/c ₂ light-harvesting complex, phycoerythrin and the -subunit of phycoerythrin. The effect of different fixation procedures on the intensity of labelling and ac curacy of antigen location have been examined and the effectiveness of uranyl acetate and tannic acid in improving both the preservation of thylakoid structure and labelling density of phycoerythrin has been demonstrated. Freeze fracture labelling gives better spatial res olution of the different antigens than post-embedding labelling, as well as better definition of thylakoid membranes. It confirms the location of phycoerythrin in the thylakoid lumen and the location of the chlorophylla/c ₂ LHC in both appressed and unappressed thylakoid membranes.Abbreviations PE phycoerythrin - chl chlorophyll - LHC light-har-vesting complex     

Nigericin forms highly stable complexes with lithium and cesium

Nigericin is a monocarboxylic polyether molecule described as a mobile K⁺ ionophore unable to transport Li⁺ and Cs⁺ across natural or artificial membranes. This paper shows that the ion carrier molecule forms complexes of equivalent energy demands with Li⁺, Cs⁺, Na⁺, Rb⁺, and K⁺. This is in accordance with the similar values of the complex stability constants obtained from nigericin with the five alkali metal cations assayed. On the other hand, nigericinalkali metal cation binding isotherms show faster rates for Li⁺ and Cs⁺ than for Na⁺, K⁺, and Rb⁺, in conditions where the carboxylic proton does not dissociate. Furthermore, proton NMR spectra of nigericin-Li⁺ and nigericin-Cs⁺ complexes show wide broadenings, suggesting strong cation interaction with the ionophore; in contrast, the complexes with Na⁺, K⁺, and Rb⁺ show only clear-cut chemical shifts. These latter results support the view that nigericin forms highly stable complexes with Li⁺ and Cs⁺ and contribute to the explanation for the inability of this ionophore to transport the former cations in conditions where it catalyzes a fast transport of K⁺>Rb⁺>Na⁺.Part of the results of this paper were presented at the 14th International Congress of Biochemistry in Prague, Czechoslovakia.     

Proton-induced grana formation in chloroplasts. Distribution of chlorophyll-protein complexes and Photosystem II photochemistry

Lowering the pH of the incubation medium to pH 5.4 leads to grana formation morphologically similar to that induced by metal cations. The same phenomenon is observed in EDTA-washed chloroplasts, indicating that it is not due in part to electrostatic ‘masking’ by residual cations associated with the membranes. Digitonin fractionation studies have indicated that the distribution of the major chlorophyll-protein complexes between granal and stromal membrane regions is similar at pH 5.4 in the absence of Mg²⁺, and at pH 7.4 in the presence of Mg²⁺. Chlorophyll fluorescence induction studies have indicated that the primary photochemistry of Photosystem II (PS II) is stimulated by lowering the pH to 5.4, just as it is upon metal cation addition at higher pH values. The failure to observe such an increase at pH 5.4 by measuring electron transport to ferricyanide is attributed to a combination of an inhibition by this pH of electron transport at a site after Q reduction and an increase in the number of PS II centres detached from the plastoquinone pool. We conclude that the stacked configuration of chloroplast membranes leads to increased PS II primary photochemistry, which is most simply explained in terms of a redistribution of excitation energy towards PS II.     

Binding of nickel (II) to 5′-nucleoside monophosphates and related compounds

Summary The interactions of Ni(II) cation with a representative suite of purine bases and the respective nucleosides and nucleotides have been studied by ultraviolet difference spectroscopy. Apparent association constants, K_app, were determined for each system at pH 7.0, using computer linear regression coupled with an iteration technique. The specificity of binding of Ni²⁺ for the purine nucleotides studied at pH 7.0 was 5-GMP > 5-IMP > 5-AMP; a similiar ordering was also found for the respective nucleosides and bases. In this study binding was not observed for the suite of pyramidines used, although a Ni²⁺ - cytidine complex has been observed (Fiskin and Beer, 1965). It was also found that Ni²⁺ bound more strongly to the purine 5-nucleotides than to the respective nucleosides and bases. These trends are explained in terms of metal-ligand bonds and available bonding positions on the ligands. A role for metal-ion-nucleotide types of complexes is suggested in the processes that might have given rise to the origin of life.     

Development and pigmentation of chlorosomes in Chloroflexus aurantiacus strain Ok-70-fl

The development of chlorosomes and their pigmentation were studied by growing Chloroflexus aurantiacus strain Ok-7o-fl first under conditions under which BChl c-synthesis is low (50°C, 2000 lux and 30°C, 1500 lux) and subsequently under conditions promoting high BChl c-synthesis (50°C, 400 lux). Electron microscopic observations on and chemical analyses of isolated cell components showed that in BChl c-depleted cells chlorosome-like structures (chlorosome bags) are attached to fragments of cytoplasmic membranes. These chlorosome bags exhibit a periodic fine structure caused by the construction of the baseplates of the chlorosomes. The baseplates are closely attached to the cytoplasmic membrane, they are rich in phospholipids and apparently contain a 790 nm-BChl a-complex. Chlorosome bags of BChl c-depleted cells always contain a limited amount of light-harvesting pigment complexes (BChlc, - and -carotene). The light-harvesting system is restored (50°C, 400 lux) by first refilling the existing chlorosome bags before cell division takes place.Abbreviations BChl Bacteriochlorophyll - LH Light-harvesting complex - RC Reaction center     

Regulation of B lymphocyte activation by the Fc portion of immunoglobulin

Murine splenic B lymphocytes are induced to proliferate and undergo polyclonal activation in the presence of Fc fragments, AHGG, antigen-antibody complexes, and CH₃ fragments derived from plasmin digestion of human Ig. The unifying feature of the polyclonal antibody response induced by these agents is that in all cases a portion of the constant region of the Ig molecule (ie, Fc region) is present. Fragments of Ig lacking the Fc piece, such as Fab and F(ab′)₂ were found not to be stimulatory. In addition, a model is proposed to account for the regulatory effects of antigen-antibody complexes on an ongoing humoral immune response.     

The action of proteolytic enzymes on chloroplast thylakoid membranes

Envelope- and stroma-free thylakoid membranes of Vicia faba chloroplasts were incubated with trypsin or pronase for several hours. The indigestible residue was analyzed by polyacrylamide gel electrophoresis. Trypsinization resulted in a complete digestion of all proteins with the exception of the pigment-protein complexes as well as a polypeptide not yet characterized. Yet, as compared with untreated material, Complex II was found to have higher electrophoretic mobility. Electron-microscopic studies illustrate that the indigestible residue still has a preserved membrane structure. Disintegration of the thylakoid membranes by sodium dodecyl sulfate followed by trypsinization also resulted in the two complexes while all the other proteins were found to be digested. However, after removal of the lipids the protein moieties of the complexes proved to be easily digestible. From these results it is concluded that pigment-protein interaction may be an important factor in maintaining a conformation rather resistant to perturbants and proteases. In contrast to trypsin, pronase completely digested the polypeptides of the thylakoid membranes including the protein moieties of the pigment-protein complexes leaving an amorphous lipid mass. The results support the assumption that the complexes are necessary to maintain the membrane structure.     

Some peculiar synaptic complexes in the first visual ganglion of the fly,Musca domestica

Summary In the lamina ganglionaris, the first optic ganglion of the fly, the inventory of cell types as well as the patterns of their connections are well known from light microscopic investigations. Even the synaptic contacts are known with relative completeness. However, the structural details visible on electron micrographs are very difficult to interpret in functional terms. This paper concentrates on two aspects: 1) the synaptic complex between a retinula cell axon and four postsynaptic elements, arranged in a constant elongated array (it is suggested that all synapses in which the retinula cell is presynaptic are of this kind), and 2) the gnarl complex in which a presynaptic specialization in one neuron is separated from another neuron by a complicated glial invagination. The participation of glia at postsynaptic sites seems to be quite common in this ganglion. Occasionally it seems that a glia cell is the only postsynaptic partner facing a presynaptic specialization within a neuron.