Current perceptions of Photosystem II

In the last few years our knowledge of the structure and function of Photosystem II in oxygen-evolving organisms has increased significantly. The biochemical isolation and characterization of essential protein components and the comparative analysis from purple photosynthetic bacteria (Deisenhofer, Epp, Miki, Huber and Michel (1984) J Mol Biol 180: 385–398) have led to a more concise picture of Photosystem II organization. Thus, it is now generally accepted that the so-called D1 and D2 intrinsic proteins bind the primary reactants and the reducing-side components. Simultaneously, the nature and reaction kinetics of the major electron transfer components have been further clarified. For example, the radicals giving rise to the different forms of EPR Signal II have recently been assigned to oxidized tyrosine residues on the D1 and D2 proteins, while the so-called Q₄₀₀ component has been assigned to the ferric form of the acceptor-side iron. The primary charge-separation has been meaured to take place in about 3 ps. However, despite all recent major efforts, the location of the manganese ions and the water-oxidation mechanism still remain largely unknown. Other topics which lately have received much attention include the organization of Photosystem II in the thylakoid membrane and the role of lipids and ionic cofactors like bicarbonate, calcium and chloride. This article attempts to give an overall update in this rapidly expanding field.     

Affinity purification of bacterial luciferase and NAD(P)H:FMN oxidoreductases by FMN-sepharose for analytical applications

A modified purification method for bacterial luciferases and NAD(P)H:FMN oxidoreductases is described which uses FMN-Sepharose alone or coupled to DEAE ion exchange chromatography for the simultaneous purification of luciferase and the various oxidoreductases from Vibrio harveyi, a bright mutant of Vibrio harveyi, Vibrio fischeri, and Photobacterium phosphoreum. This purification method is compared with DEAE-Sepharose CI 6B fractionations from these organisms. Both methods allow the separation of oxidoreductases specific for either NADH or NADPH. The use of FMN-Sepharose coupled to DEAE-Sepharose fractionation allows the isolation of highly purified enzymes. Lacking interfering factors, these are very suitable for various analytical applications based on bacterial bioluminescence enzymes. The partially purified enzymes from the affinity column have higher specific activities than those obtained using DEAE-Sepharose.     

EagI andNotI linking clones from human chromosomes 11 and Xp

EagI and NotI linking libraries were prepared in the lambda vector, EMBL5, from the mouse-human somatic cell hybrid 1W1LA4.9, which contains human chromosomes 11 and Xp as the only human component. Individual clones containing human DNA were isolated by their ability to hybridise with total human DNA and digested with SalI and EcoRI to identify the human insert size and single-copy fragments. The mean (± SD) insert sizes of the EagI and NotI clones were 18.3 ± 3.2 kb and 16.6 ± 3.6 kb, respectively. Regional localisation of 66 clones (52 EagI, 14 NotI) was achieved using a panel of 20 somatic cell hybrids that contained different overlapping deletions of chromosomes 11 or Xp. Thirty-nine clones (36 EagI, 3 NotI) were localised to chromosome 11; 17 of these were clustered in 11q13 and another nine were clustered in 11q14–q23.1. Twenty-seven clones (16 EagI, 11 NotI) were localised to Xp and 10 of these were clustered in Xp11. The 66 clones were assessed for seven different microsatellite repetitive sequences; restriction fragment length polymorphisms for five clones from 11q13 were also identified. These EagI and NotI clones, which supplement those previously mapped to chromosome 11 and Xp, should facilitate the generation of more detailed maps and the identification of genes that are associated with CpG-rich islands. Received: 27 December 1995 / Revised: 30 January 1996     

Changes in extracellular levels of dopamine metabolites in somatosensory cortex after peripheral denervation

This study examined the effects of a nerve transection on monoamine release from primary somatosensory cortex. The technique of microdialysis was employed to sample extracellular levels of norepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindole-3-acetic acid (5-HIAA) and homovanillic acid (HVA) in the barrel field of freely moving rats following the surgical transection of the contralateral infraorbital nerve. Microdialysates obtained 3, 4, and 5 days after deafferentation were analyzed using high-performance liquid chromatography with electrochemical detection. We found a significant increase in the release of the dopamine metabolites, DOPAC and HVA from the deafferented cortex. Three days after deafferentation the release of DOPAC was three-fold higher in the deafferented than in the control animals, and remained about 100% higher in the next two days in this group of animals. The release of HVA showed a gradual increase following the deafferentation procedure, since a 92% larger value on day 3 increased to a 338% difference on day 5. On the other hand, the release rate of NE and the levels of the serotonin metabolite 5-HIAA were not significantly affected by the deafferentation procedure. These results are discussed in the context of the possible participation of dopamine in the reorganization of the deafferented somatosensory cortex.     

Social Learning of a Novel Foraging Skill by White-throated Magpie-jays (Calocitta formosa,Corvidae): a Field Experiment

The cooperatively breeding white-throated magpie-jay (Calocitta formosa) uses a variety of foraging tactics to find, harvest, and process food. Members of territorial groups forage together and may gain information about how to acquire food by observing each other. A field experiment was performed to determine whether a novel skill, door opening to gain access to food, was more rapidly acquired by members of groups in which a trained individual performed the skill. A higher proportion of jays in groups with behavioural ‘models’ (trained birds that opened doors in the presence of group members) acquired the door-opening skill than those groups without models. Young birds acquired the behaviour more frequently than older individuals. Aggressive behaviour at feeders may have affected the spread of the behaviour by reducing the likelihood that individuals performed the behaviour in the presence of other group members but may also have encouraged subordinate individuals to attempt door opening rather than ‘scrounge’.     

Application of the integrated lake-watershed acidification study model to watershed liming at woods Lake,New York

Woods Lake, in the Adirondack Mountains of New York, was the site of the Experimental Watershed Liming Study (EWLS) in which base addition was investigated as a method for mitigation of lake acidity. In an effort to predict the duration of effects, the treatment was simulated using the Integrated Lake-Watershed Acidification Study (ILWAS) model. To simulate terrestrial liming, calcite was applied to treated subcatchments as a rapidly weathering mineral in the upper horizon. Soil solution and lake outlet chemistry showed a response to calcite addition within four months of the start of the simulation. Calcium concentrations, acid neutralizing capacities (ANC), and pH increased in the upper soil layer and aluminum concentrations decreased in the upper three soil layers (0–70 cm). The response of ANC was delayed in lower soil layers due to proton production associated with aluminum hydrolysis. Moreover, soil water pH in the third soil layer decreased in response to calcite treatment due to the displacement of hydrogen ions by calcium added to the exchange complex. Calcium concentrations, ANC and pH increased and aluminum concentrations decreased in the simulated lake outlet. The modeled effects of calcite treatment on the soil and lake outlet chemistry were not as great as field observations. This was, in part, attributed to the model representation of the watershed, which did not include streams, ponds, or wetlands located in the treated subcatchments. Calcite applied to these saturated areas in the field readily dissolved, supplying ANC to lake water. Additionally, incorporation of calcite into a thick organic layer in the model diminished the possibility of dissolution by contact with overland flow. Observed concentrations of calcium, ANC, and pH in the outlet decreased after high values in the two years after treatment. Although the model failed to match observed short-term data, it may simulate the long-term response as calcium is transported through the soil. A long-term simulation of the model suggests that effects of base treatment will persist for at least 50 years.     

Six things Popper would like biologists not to ignore: In memoriam, Karl Raimund Popper, 1902–1994

To honour the memory of Sir Karl Popper, I put forward six elements of his philosophy which might be of particular interest to biologists and to philosophers of biology and which I think Popper would like them not to ignore, even if they disagree with him. They are: the primacy of problems; the criticizability of metaphysics (and thus the dubiousness of materialism); how downward causation might be real; how norms should matter to scientists; why dogmatism should be avoided; how genuine science is recognizable. I preface these six things with a brief discussion of Popper's early (but later recanted) mistakes concerning biology.     

Effect of concentration and environmental form of tetradecenyl succinic acid on its mineralization in soil

Tetradecenyl succinic acid (TSA) is the major component of a detergent builder (C12-C14 alkenyl succinic acid), which is inherently biodegradable. ¹⁴C-TSA was dosed as a component of sewage sludge into a soil with a history of sludge amendment at final added concentrations of 1.5 and 30 mg (kg soil)^-1. In addition, it was dosed to the soil in an aqueous solution to a final added concentration of 30 mg (kg soil)^-1. Dose and form were found to have a pronouced effect on the mineralization kinetics. When dosed in a realistic form and concentration (i.e. 1.5 mg (kg soil)^-1 as a component of sludge), TSA was mineralized at its highest rate and to its greatest extent, and the mineralization half-life was 2.4 days. When dosed at 30 mg (kg soil)^-1 as a component of sludge, mineralization began immediately, and the half-life was 23 days. In contrast, when dosed at this concentration in aqueous solution, the onset of mineralization was preceded by a 13 day lag period and the mineralization half-life was 69 days. Primary biodegradation and mineralization rates of TSA were very similar. Approximately, half the radioactivity was evolved as ¹⁴CO₂, while the remaining radioactivity became non-extractable, having presumably been incorporated into biomass or natural soil organic matter (humics). This study demonstrated that TSA is effectively removed from sludge-amended soils as a result of biodegradation. Furthermore, it showed the effect that dose form and concentration have on the biodegradation kinetics and the importance of dosing a chemical not only at a relevant concentration but also in the environmental form in which it enters the soil environment.     

Flocculation of industrial and laboratory strains ofSaccharomyces cerevisiae

Summary A comparative study has been made of different laboratory and industrial wild-type strains ofSaccharomyces cerevisiae in relation to their flocculation behavior. All strains were inhibited by mannose and only one by maltose. In regard to the stability of these characters in the presence of proteases and high salt concentrations, a relevant degree of variation was found among the strains. This was to such an extent that it did not allow their inclusion in the Flol or NewFlo phenotypes. Genetic characterization of one wild-type strain revealed that the flocculation-governing gene was allelic toFLO1 found in genetic strains.This paper is dedicated to Professor Herman Jan Phaff in honor of his 50 years of active research which still continues.     

Genetic conflict and evolution of mammalian X-chromosome inactivation

The existence of parentally imprinted gene expression in the somatic tissues of mammals and plants can be explained by a theory of intragenomic genetic conflict, which is a logical extension of classical parent-offspring conflict theory. This theory unites conceptually the phenomena of autosomal imprinting and X-chromosome inactivation. We argue that recent experimental studies of X-chromosome inactivation and andro-genetic development address previously published predictions of the conflict theory, and we discuss possible explanations for the occurrence of random X-inactivation in the somatic tissues of eutherians. © 1995 Wiley-Liss, Inc.