Structure of donor side components in photosystem II predicted by computer modelling.

Thirty-one and eleven sequences for the photosystem II reaction centre proteins D1 and D2 respectively, were compared to identify conserved single amino acid residues and regions in the sequences. Both proteins are highly conserved. One important difference is that the lumenal parts of the D1 protein are more conserved than the corresponding parts in the D2 protein. The three-dimensional structures around the electron donors tyrosineZ and tyrosineD on the oxidizing side of photosystem II have been predicted by computer modelling using the photosynthetic reaction centre from purple bacteria as a framework. In the model the tyrosines occupy two cavities close to the lumenal surface of the membrane. They are symmetrically arranged around the primary donor P680 and the distances between the centre of the tyrosines and the closest Mg ion in P680 are around 14 A. Both tyrosineZ and tyrosineD are suggested to form a hydrogen bond with histidine 190 from the loop connecting helices C and D in the D1 and D2 proteins, respectively. The Mn cluster in the oxygen evolving complex has been localized by using known and estimated distances from the tyrosine radicals. It is suggested that a binding region for the Mn cluster is constituted by the lumenal ends of helices A and B and the loop connecting them in the D1 protein. This part of the D1 protein contains a large number of strictly conserved carboxylic acid residues and histidines which could participate in the Mn binding. There is little probability that the Mn cluster binds on the lumenal surface of the D2 protein.     

Effect of aluminium on iron uptake and transferrin-receptor expression by human erythroleukaemia K562 cells.

Incubation of human erythroleukaemia K562 cells with Al-transferrin inhibited iron uptake from 59Fe-transferrin by about 80%. The inhibition was greater than that produced by a similar quantity of Fe-transferrin. Preincubation of cells for 6 h with either Al-transferrin or Fe-transferrin diminished the number of surface transferrin receptors by about 40% compared with cells preincubated with apo-transferrin. Al-transferrin did not compete significantly with Fe-transferrin for transferrin receptors and, when cells were preincubated for 15 min instead of 6 h, the inhibitory effect of Al-transferrin on receptor expression was lost. Both forms of transferrin also decreased the level of transferrin receptor mRNA by about 50%, suggesting a common regulatory mechanism. Aluminium citrate had no effect on iron uptake or transferrin-receptor expression. AlCl3 also had no effect on transferrin-receptor expression, but at high concentration it caused an increase in iron uptake by an unknown, possibly non-specific, mechanism. Neither Al-transferrin nor AlCl3 caused a significant change in cell proliferation. It is proposed that aluminium, when bound to transferrin, inhibits iron uptake partly by down-regulating transferrin-receptor expression and partly by interfering with intracellular release of iron from transferrin.     

Thermoluminescence from the photosynthetic apparatus

One of the fundamental discoveries of W. Arnold was the detection of thermally stimulated light emission from preilluminated photosynthetic material (Arnold and Sherwood (1957) Proc Natl Acad Sci USA 43: 105–114). This phenomenon, called thermoluminescence (TL), is characteristic of a wide range of materials (semiconductors, minerals, inorganic and organic crystals, and complex biological systems such as the photosynthetic apparatus) which share the common ability of storing radiant energy in thermally stabilized trap states.The original discovery of TL in dried chloroplasts later proved to be a phenomenon common to all photosynthetic organisms: photosynthetic bacteria, cyanobacteria, algae and higher plants. Following the pioneering work of Arnold, considerable effort has been devoted to identification and characterization of photosynthetic TL components. This work has firmly established the participation of various redox states of the water-oxidizing complex and the quinone electron acceptors of Photosystem II in the generation of photosynthetic glow curves. Since TL characteristics are very sensitive to subtle changes in redox properties of the involved electron transport components, the TL method has become a powerful tool in probing a wide range of PS II redox reactions. In this paper, we will review the impact of Arnold's work in initiating and promoting TL studies in photosynthesis and will cover the most important developments of this field of research until the present day.Abbreviations Chl chlorophyll - DL delayed luminescence - PS photosystem - TL thermoluminescence     

Calcium/Calmodulin-Stimulated Protein Kinase II Is Present in Primary Cultures of Cerebral Endothelial Cells

Abstract: Calcium/calmodulin-stimulated protein kinase II (CaMPK II). a major kinase in brain, has been established to play an important role in neurotransmitter release and organization of postsynaptic receptors, and it is known to be involved in long-term potentiation and memory. Less is known about the function of this enzyme in nonneural cells. Here we report on the production, presence, and phosphorylation of the α-subunit of CaM-PK II in primary cultures of cerebral endothelial cells. These results raise the possibility that α-CaM-PK II can act as one of the key enzymes of calcium-mediated intracellular signaling in the cerebral endothelial cells and suggest that α-CaM-PK II may participate in such basic cellular processes as permeability in physiological and pathological conditions.     

Endolithic microbial life in hot and cold deserts

Endolithic microorganisms (those living inside rocks) occur in hot and cold deserts and exist under extreme environmental conditions. These conditions are discussed on a comparative basis. Quantitative estimates of biomass are comparable in hot and cold deserts. Despite the obvious differences between the hot and cold desert environment, survival strategies show some common features. These endolithic organisms are able to switch rapidly their metabolic activities on an off in response to changes in the environment. Conditions in hot deserts impose a more severe environmental stress on the organisms than in the cold Antarctic desert. This is reflected in the composition of the microbial flora which in hot desert rocks consist entirely of prokaryotic microorganisms, while under cold desert conditions eukaryotes predominate.Proceedings of the Fourth College Park Colloquium on Chemical Evolution:Limits of Life, University of Maryland, College Park, 18–20 October 1978.     

Restriction endonuclease analysis of the transducing bacteriophage lambda rif d18

The rif d18 bacteriophage carries essential parts of the E. coli genome which can not be mapped by conventional methods. The phage DNA was analysed with four restriction endonucleases (endo R. BamHI, Sall, HpaI and EcoRI) and a physical map was constructed.     

Comparison of the genomic organization of Kirsten and Harvey sarcoma viruses.

Current studies were undertaken to compare the genomes of Kirsten murine sarcoma virus (Ki-MuSV), Harvey murine sarcoma virus (Ha-MuSV), and the replication-defective endogenous rat virus to understand the function of these viral RNAs. Genome organization and sequence homology were studied by fingerprinting large RNase T1-resistant oligonucleotides and by cross-protecting homologous oligonucleotides against RNase A and T1 digestion with complementary DNA prepared from each of the other viral RNA. Ki-MuSV and Ha-MuSV were found to share an extensive series of rat-derived oligonucleotides begining ca. 1 kilobase (kb) from the 3' end and extending to within 1.5 kb of the 5'end of Ki-MuSV RNA. The total map distance covered in ca. 5.5 kb. The eight oligonucleotides covering the 1.5 kb at the 5' end of Ki-MuSV RNA were not found in Ha-MuSV RNA. Five out of these eight oligonucleotides, however, could be designated with certainty to be of rat virus origin. Since Ha-MuSV is 6.5 kb in size and Ki-MuSV is 8 kb in size, the major difference between them is the 1.5 kb from the replication-defective endogenous rat virus sequences at the 5' end of Ki-MuSV not present in Ha-MuSV. Consistent with the difference in the genome structure, these two sarcoma viral RNA'S yielded distinct major translation products in cell-free systems, I.E., A 50,000-dalton polypeptide (P50) from Ki-MuSV and a 22,000-dalton polypeptide (p22) from Ha-MuSV. These polypeptides may provide the necessary protein makers for identifying in vivo virus-coded proteins.     

The role of N-acyl groups in the inhibitory activity of LH-RH analogues

Inhibitory analogues of luteinizing hormone-releasing hormone (LH-RH) were prepared with formyl-D-Trp¹, acetyl-D-Trp¹, valeryl-D-Trp¹, tartaryl-D-Trp¹, diacetyl-tartaryl-D-Trp¹, acetyl-Gly¹, and acetyl-Sar¹ successively replacing the position one in the analogue [D-Trp¹, D-p-Cl-Phe², D-Trp³, D-Phe⁶, D-Ala¹⁰]-LH-RH. The formyl-D-Trp¹ and acetyl-D-Trp¹ analogues yielded 100% blockade of ovulation at the 10 μg dose; the others were less potent and inhibited ovulation at the 50 μg dose. The inhibitory potency seems to correlate with the polarity of the acyl group.     

Immortalization of murine primary spleen cells by v-myc, v-ras, and v-raf.

Growth factor-independent cell lines, including four lines characterized as macrophages, were isolated by infection of BALB/c mouse primary spleen cells with combinations of three retroviruses encoding v-myc, v-ras, and v-myc/v-raf. Proliferating cell lines were isolated only rarely, and after long crisis periods, following the introduction of myc and raf by infection with J2 virus, or of myc and ras by coinfection with myc309 and raszip6 viruses. However, sequential infections with all three viruses--myc plus ras cells reinfected with J2, or J2 followed by myc plus ras coinfection--resulted in rapid outgrowth of cell lines which grew at high growth rates to high densities. When cells were treated with anti-IgG F(ab')2/IL-4/IL-5 to specifically stimulate B cells, cell lines were isolated readily by infection with myc plus ras alone, J2 alone, or all three viruses. These cell lines arose after shorter crisis times and all grew at high growth rates and to high densities. Analysis of cell surface markers and immunoglobulin gene arrangement revealed no lymphoid characteristics in any of the lines. Four cell lines express all three macrophage markers analyzed (F4/80, Mac1, FcR), and many others are Mac1+ and/or FcR+. Out of 20 immortalized cell lines tested, 13 show clonal growth in soft agar, and 3/6 of these produced tumors in BALB/c mice, indicating that fully transformed cells may be isolated by these procedures. In at least one of the cell lines, integration of all three infecting viruses has occurred.