Taxonomic distribution and origins of the extended LHC (light-harvesting complex) antenna protein superfamily

Background  

The extended light-harvesting complex (LHC) protein superfamily is a centerpiece of eukaryotic photosynthesis, comprising the LHC family and several families involved in photoprotection, like the LHC-like and the photosystem II subunit S (PSBS). The evolution of this complex superfamily has long remained elusive, partially due to previously missing families.     

High concentrations of exogenous arachidonate inhibit calcium mobilization in platelets by stimulation of adenylate cyclase.

1. Exposure of platelets to exogenous arachidonic acid results in aggregation and secretion, which are inhibited at high arachidonate concentrations. The mechanisms for this have not been elucidated fully. In our studies in platelet suspensions, peak aggregation and secretion occurred at 2-5 microM-sodium arachidonate, with complete inhibition around 25 microM. 2. In platelets loaded with quin2 or fura-2, the cytoplasmic Ca2+ concentration, [Ca2+]i, rose in the presence of 1 mM-CaCl2 from 60-80 nM to 300-500 nM at 2-5 microM-arachidonate, followed by inhibition to basal values at 25-50 microM. Thromboxane production was not inhibited at 25 microM-arachidonate. Cyclic AMP increased in the presence of theophylline, from 3.5 pmol/10(8) platelets in unexposed platelets to 8 pmol/10(8) platelets at 50 microM-arachidonate; all platelet responses were inhibited with doubling of cyclic AMP contents. 3. The adenylate cyclase inhibitor 2',5'-dideoxyadenosine attenuated the inhibitory effect of arachidonate, suggesting that it is mediated by increased platelet cyclic AMP and that it is unlikely to be due to irreversible damage to platelets. 4. Aspirin or the combined lipoxygenase/cyclo-oxygenase inhibitor BW 755C did not prevent the inhibition by arachidonate of either [Ca2+]i signals or aggregation induced by U46619. 5. Thus high arachidonate concentrations inhibit Ca2+ mobilization in platelets, and this is mediated by stimulation of adenylate cyclase. High arachidonate concentrations influence platelet responses by modulating intracellular concentrations of two key messenger molecules, cyclic AMP and Ca2+.     

The use of a resin adsorbent to isolate cytokinins from sea water

XAD-4 resin was used to isolate cytokinins present in Baltic sea water. Four compounds were tentatively identified as 6-(3-methylbut-2-enylamino) purine and zeatin, and their ribosides.     

Megachromosomes in tissue culture ofAllium

Chromosome studies have been conducted on the long-term callus cultures of threeAllium species:A. porrum (2n=32),A. tuberosum (2n=32) andA. fistulosum (2n=16). In cultures ofA. fistulosum several interesting cytological abnormalities were observed. They included direct elimination of chromatin from nuclei, multiple chromosome fusions and formation of polycentric and megachromosomes. The rate of abnormalities increased with the time of culture. Allium fistulosum may provide an excellent model system to analyse cytogenetic and molecular aspects of callus-induced genomic changes and, thus, somaclonal variation.     

Sequence analysis of mitochondrial chloramphenicol resistance mutations in Chinese hamster cells

A series of mitochondrially inherited chloramphenicol-resistant (CAP-R) mutants were isolated in Chinese hamster cells. To determine whether the Chinese hamster CAP-R mutations were homologous to those isolated in mouse and human cell culture systems, we determined the nucleotide sequence of the region of the mitochondrial 16S rRNA gene spanning the peptidyl transferase-encoding region for eight CAP-R mutant lines in addition to the parental wildtype line. Three main conclusions are drawn from these studies. (1) Although the region of the gene encoding the peptidyl transferase domain is highly conserved relative to that of mice and rats, the contiguous sequences show less conservation. This sequence divergence not only includes the accumulation of single base pair replacements, but also the presence of small insertions or deletions. (2) For six of the CAP-R mutants, heteroplasmic single base pair changes were detected. These mapped to the same sites within the peptidyl transferase domain as the mutations found previously in mouse and human CAP-R mutants. (3) Two Chinese hamster CAP-R mutants, both with an unusual drug resistance phenotype, did not carry any mutations within the CAP-R peptidyl transferase domain. However, both carried a heteroplasmic mutation at the position corresponding to nucleotide 2505 of the mouse 16S rRNA gene, a site predicted to map within a stem/loop structure attached to this key domain of the ribosome. This is the first evidence for mitochondrial CAP-R mutations that map outside the peptidyl transferase region.     

Serum concentration of prolactin, gastrin and glycocholic acid in patient with peptic ulcer treated with ranitidine

In 66 patients with peptic ulcer (11 with gastric ulcer, 55 with duodenal ulcer, 19 women, 47 men) the serum concentrations of prolactin, dehydrocholic acid and gastrin were determined. The studies were repeated after treatment with ranitidine: in 50 patients after three weeks and in 40 patients after another 30 days. During the first period ranitidine 2 x 150 mg was administered, while during the second period the dose was 1 x 150 mg. The results were compared with those obtained from 120 healthy subjects. Before starting the treatment prolactin levels were significantly higher than those in the control group. During the treatment a significant decrease of the levels was observed. Similar changes of prolactin concentrations were found in the group of 39 men with duodenal ulcer isolated from the studied patients, who were compared with a group of 50 healthy men. It was not found that the development of peptic ulcer and the treatment with ranitidine exerted and effect on the changes of gastrin and dehydrocholic acid concentrations.     

The influence of macrophytes on a phytoplankton community in experimental conditions

The impact of submerged macrophytes or their extracts on planktonic algae was studied under experimental conditions. Live Ceratophyllum demersum L., its extract, and extracts of four other plant species induced modifications in the phytoplankton dominance structure. These modifications were: a decline in the number of Oscillatoria limnetica Lemm., which was the most numerous cyanobacterian species, and a decline in biomass and percentage contribution of all cyanobacteria to total algal biomass. This was accompanied by an increase in biomass and percentage contribution of green algae, especially Chlorella sp. and Chlamydomonas sp. Also, there was an increase in biomass and percentage contribution of nanoplankton (under 50 µm) to total phytoplankton biomass.The isolation of planktonic algae from direct influence of C. demersum by means of dialysis membranes caused an increase in number, biomass and percentage contribution of cyanobacteria. Release of organic compounds of over 3000 daltons by macrophytes apparently contributed to a decline of cyanobacteria by changing the phytoplankton dominance structure.     

E.s.r. radiation studies of erythrocyte membrane haemoglobin interaction.

The dependence of the yield of free radicals in gamma-irradiated, freeze-dried erythrocyte membranes on their haemoglobin content was studied. A non-monotonous relationship was found--different from that observed in mixtures of freeze-dried membranes and haemoglobin, which suggests the existence of radiation-energy transfer between the membranes and bound haemoglobin.     

mRNAs containing the histone 3′ stem–loop are degraded primarily by decapping mediated by oligouridylation of the 3′ end

Metazoan replication-dependent histone mRNAs are only present in S-phase, due partly to changes in their stability. These mRNAs end in a unique stem–loop (SL) that is required for both translation and cell-cycle regulation. Previous studies showed that histone mRNA degradation occurs through both 5′→3′ and 3′→5′ processes, but the relative contributions are not known. The 3′ end of histone mRNA is oligouridylated during its degradation, although it is not known whether this is an essential step. We introduced firefly luciferase reporter mRNAs containing the histone 3′ UTR SL (Luc-SL) and either a normal or hDcp2-resistant cap into S-phase HeLa cells. Both mRNAs were translated, and translation initially protected the mRNAs from degradation, but there was a lag of ∼40 min with the uncleavable cap compared to ∼8 min for the normal cap before rapid decay. Knockdown of hDcp2 resulted in a similar longer lag for Luc-SL containing a normal cap, indicating that 5′→3′ decay is important in this system. Inhibition of DNA replication with hydroxyurea accelerated the degradation of Luc-SL. Knockdown of terminal uridyltransferase (TUTase) 4 but not TUTase 3 slowed the decay process, but TUTase 4 knockdown had no effect on destabilization of the mRNA by hydroxyurea. Both Luc-SL and its 5′ decay intermediates were oligouridylated. Preventing oligouridylation by 3′-deoxyadenosine (cordycepin) addition to the mRNA slowed degradation, in the presence or absence of hydroxyurea, suggesting oligouridylation initiates degradation. The spectrum of oligouridylated fragments suggests the 3′→5′ degradation machinery stalls during initial degradation, whereupon reuridylation occurs.