The mechanism of photosynthetic water oxidation

Photosynthetie water oxidation is unique to plants and cyanobacteria, it occurs in thylakoid membranes. The components associated with this process include: a reaction center polypeptide, having a molecular weight (Mr) of 47–50 kilodaltons (kDa), containing a reaction center chlorophyll a labeled as P680, a plastoquinol(?)-electron donor Z, a primary electron acceptor pheophytin, and a quinone electron acceptor Q_A; three ‘extrinsic’ polypeptides having Mr of approximately 17 kDa, 23 kDa, and 33 kDa; and, in all likelihood, an approximately 34 kDa ‘intrinsic’ polypeptide associated with manganese (Mn) atoms. In addition, chloride and calcium ions appear to be essential components for water oxidation. Photons, absorbed by the so-called photosystem II, provide the necessary energy for the chemical oxidation-reduction at P680; the oxidized P680 (P680⁺), then, oxidizes Z, which then oxidizes the water-manganese system contained, perhaps, in a protein matrix. The oxidation of water, leading to O₂ evolution and H⁺ release, requires four such independent acts, i.e., there is a charge accumulating device (the so-called S-states). In this minireview, we have presented our current understanding of the reaction center P680, the chemical nature of Z, a possible working model for water oxidation, and the possible roles of manganese atoms, chloride ions, and the various polypeptides, mentioned above. A comparison with cytochrome c oxidase, which is involved in the opposite process of the reduction of O₂ to H₂O, is stressed. This minireview is a prelude to the several minireviews, scheduled to be published in the forthcoming issues of Photosynthesis Research, including those on photosystem II (by H.J. van Gorkom); polypeptides of the O₂-evolving system (by D.F. Ghanotakis and C.F. Yocum); and the role of chloride in O₂ evolution (by S. Izawa).     

Semiautomatic procedure for the investigation of synchronized activity of EEG and heart rate--examination of preterm births]

Recordings of the electroencephalogram (EEG) and of the heart rate variability (HRV) of preterm neonates can give important information on the actual state of the nervous system. Both signals, EEG and HRV, are affected by parameters such as gestational age, stage of maturation and behavioral state. This work describes a method for automatic detection of slow wave EEG-bursts and a tool to average changes in the EEG and the corresponding heart rate. The detection is based on the hjorth activity (HA), calculated from the EEG. HA spikes (HAS) are identified by the determination of the beginning and end of existing spikes. HAS maxima and the time between two consecutive HAS are the basis for the triggering of the bursts. EEG power and time synchronized HR changes are averaged with a time window length of 20 s. Resultant, HR increase and duration are determined. These parameters, obtained by the automatic detection, proved to be comparable to the results of an expert.     

Crossing the Rhine: a potential barrier to wildcat (<Emphasis Type="Italic">Felis silvestris silvestris</Emphasis>) movement?

The European wildcat (Felis silvestris silvestris) underwent a severe decline across Europe in the early twentieth century. Remaining populations are often very small and isolated, though there are indications that wildcat populations are currently expanding their range. However, linear landscape elements such as rivers and roads are thought to present barriers to dispersal, inhibiting gene flow and, thus, affecting the recolonization process. In this study, we investigated the fine-scale genetic structure of wildcats in the Upper Rhine Valley. We specifically analysed wildcats on both sides of the Rhine River by genotyping 55 individual wildcats, using 20 microsatellite loci. Genetic differentiation was weak and positive spatial autocorrelation was found up to a distance of 10 km (females: 5 km, males: 10 km) indicating substantial gene flow among sampling sites. High levels of gene flow, even across the Rhine River, indicated that the water body itself does not necessarily have a strong barrier effect, which is in contrast to other studies. Our findings could best be explained by the populations’ history, a local extinction east of the River Rhine and a current ongoing population expansion. Our study highlights that potential barriers, such as rivers, may have different effects in different local wildcat populations and that the history of the populations is important to interpret genetic results. As many wildcats still occur in isolated and patchy forest fragments, maintaining connectivity between populations is crucial to ensure their viability in the long term.     

The regulation of the energy-dependent phosphate uptake by the blue-green alga Anacystis nidulans

Investigations of the energy-dependent accumulation of orthophosphate by the blue-green alga Anacystis nidulans have established: 1. The transport through the cell membrane is the rate-limiting step in the incorporation of phosphate.-2. This transport is facilitated by a carrier that can be activated by Ca²⁺ and Mg²⁺ and inhibited by EDTA.-3. The activation of the carrier in the light is associated with changes of the cytoplasmic Mg²⁺ content.-4. Intracellular phosphate is shown to be present in bound form.-5. The energy-dependent accumulation of orthophosphate within the cell depends strictly on the cytoplasmic pH and not on the energy conversion at the thylakoid membrane which is responsible for the energy supply. The cytoplasmic pH is different in the light, in the dark, and in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). Orthophosphate accumulation can most readily be explained in terms of a pH dependent precipitation into a complex with bivalent cations rather than by an active transport against a concentration gradient.Abbreviation CCCP Carbonyl cyanide m-chlorophenylhydrazone     

Morphology and physiology of peripheral giant interneurons in the forelegs (whips) of the whip spider Heterophrynus elaphus Pocock (Arachnida: Amblypygi)

Summary The tarsi of the modified front legs (whips) of the whip spider Heterophrynus elaphus contain two afferent giant fibers, GN1 and GN2, with diameters at the tibia-tarsus joint of ca. 21 m and 14 m, respectively. The somata of these two neurons lie in the periphery, about 25 cm away from the CNS. These two neurons are interneurons which receive mechanoreceptive inputs from approximately 750 and 1500 bristles, respectively. The receptive fields of GN1 and GN2 overlap; they extend for 40 mm (GN1) and 90 mm (GN2) along the length of the tarsus. About 90% of the synapses onto the giant fibers are axo-axonic. Mechanical stimulation of a single bristle is sufficient to elicit action potentials in one or both interneurons. The response of the interneurons adapts quickly. Average conduction time from the soma to the CNS is 45 ms for GN1 and 55 ms for GN2. Mean conduction velocities are 5.5 and 4.2 m/s, respectively. Activity in the giant fibers does not elicit a motor response; hence the giant fibers do not mediate an escape response. Possible functions of these giant fibers are discussed and compared to those of giant fiber systems in other arthropods.Abbreviations GN giant neuron - S segment