Photosystem II particles largely depleted in the two intrinsic polypeptides in the 30 kDa region from Synechococcus sp. Identification of a subunit which carries the photosystem II reaction center

AbstractTreatment of oxygen-evolving photosystem II particles isolated from the thermophilic cyanobacterium, Synechococcus sp. with β-octylglucoside specifically solubilized two intrinsic polypeptides of 31 and 28 kDa from the particles. The removal of the two polypeptides had no significant effect on photoreduction of the bound quinone acceptor QA. The results indicate that the 31 and 28 kDa polypeptides are not essential for the primary charge separation and subsequent reduction of QA and hence support the view that the reaction center and QA are located on the chlorophyll-carrying 47 kDa subunit

The Hamiltonian in an Aharonov-Bohm gauge field and its self-adjoint extensions

By using the spherical coordinates in 3+1 dimensions we study the self-adjointness of the Dirac Hamiltonian in an Aharonov-Bohm gauge field of an infinitely thin magnetic flux tube. It is shown that the angular part of the Dirac Hamiltonian requires self-adjoint extensions as well as its radial one. The self-adjoint extensions of the angular part are parametrized by 2x2 unitary matrix.Comment: 10 pages, late

A simple procedure to determine Ca2+ in oxygen-evolving preparations from Synechococcus sp

AbstractA simple procedure to determine Ca2+ bound to low- and high-affinity sites of Synechococcus oxygen-evolving particles was developed. The method consists of determination of Ca2+ in the particle suspensions with and without treatment with a chelating resin, Chelex 100, to remove the metal cations contaminating the suspension medium as well as those weakly bound to the particles. It was found that the particles contain one tightly bound Ca2+ per PS II reaction center which cannot be extracted with Chelex 100 and a larger amount of weakly associated and resin-extractable Ca2+

CALCIUM MODULATION OF THE SPONTANEOUS ACTIVITY AND THE IONIC CURRENTS IN RABBIT ATRIO-VENTRICULAR NODAL CELLS

Modulation by changing the extracellular Ca²⁺ concentration ([Ca]ₒ) of the electrophysiological activity in isolated rabbit atrio-ventricular (AV) nodal cells was investigated using the two-microelectrode voltage-clamp technique. Low [Ca]ₒ (0.9 mM or Ca²⁺-free) decreased the rate of spontaneous beating, but the maximum rate of depolarization was significantly enhanced. Simultaneously, the [Ca]ₒ decline tended to increase the action potential amplitude, prolong the action potential duration (at 50% repolarization), and shorten the cycle length. The maximum diastolic potential was hyperpolarized. But these factors were not significant. In contrast, elevation of [Ca]ₒ to 5.4 or 10 mM (from 1.8 mM) transiently stimulated, but then inhibited the spontaneous activity. The effects on the action potential parameters were rather depressant. In voltage-clamp experiments, the [Ca]ₒ elevation increased the maximum onductances for the slow inward current and the delayed outward K⁺ current, whereas the [Ca]ₒ decline decreased them. An arrhythmia occurred in 4 out of 6 preparations only at 10 mM [Ca]ₒ. These results indicate that [Ca]ₒ would modulate the electrical activity of the AV nodal cells due to conductance changes in the ionic channels, but high [Ca]ₒ induces rather the depressant effects

CARDIOPROTECTIVE ACTION OF AMILORIDE, A POTASSIUM SPARING DIURETIC DRUG, IN CANINE VENTRICULAR MUSCLE

Electrophysiological and mechanical effects and alteration of intracellular Ca²⁺ concentration in canine ventricular muscle by amiloride, a potassium sparing diuretic drug, were examined, using conventional microelectrode technique and fura-2 Ca²⁺-sensitive fluorescent dye. Amiloride (50 μM) depressed the action potential amplitude by 8.2±1.4% (n=8, P<0.05) and the maximum rate of depolarization by 16.2±2.0% (n=8, P<0.01). In addition, the action potential duration was prolonged by 26.7±3.4% (n=6, P<0.05) at 30 μM, and the resting potential was depolarized by 11.8±1.7% (n=6, P<0.05) at 0.5 mM amiloride. In contrast, amiloride (0.5 to 1 mM) significantly increased the contractile force by 8 to 30% (n=8), but tended to decrease it at lower concentrations (30 μM to 0.1 mM). The positive inotropic effect was not affected by propranolol (0.1 μM), a β-adrenoceptor blocker. In fura-2 loaded ventricular myocytes, amiloride (1 mM) initially elevated cellular Ca²⁺ level ([Ca]₁) by 24.5±2.9% (n=6, P<0.01), and during the application, the [Ca]₁ level declined. These results indicate that amiloride possesses complex cardiac (protective) actions : electrical inhibitory and mechanical stimulatory actions, accompanied with the elevation of cellular Ca²⁺ concentration

PROTON MODULATIONS ON THE IONIC CURRENTS IN RABBIT ATRIO-VENTRICULAR NODAL CELLS

Modulations of changing the extracellular pH on the electrophysiological activity of isolated rabbit atrio-ventricular (AV) nodal cells were investigated using the two microelectrode voltage-clamp technique. Increasing pH from 7.4 to 9.5 enhanced spontaneous activity. The action potential amplitude and the maximum rate of depolarization were decreased. The action potential duration at 50% repolarization and the cycle length were shortened. The maximum diastolic potential was hyperpolarized. The pH elevation increased the maximum conductances for both the slow inward current and the delayed outward current systems. In contrast, a decline of pH from 7.4 to 5.5 inhibited the activity and the ionic currents. The effects on the action potential parameters were reversed. However, both acidification and alkalinization failed to affect the gating kinetics of the channels. These results suggest that H⁺ would modulate the electrical activity of the AV nodal cells, due not to an alteration of the membrane surface charge, but to a direct protonation of the ionic channels

Tolerance to freezing stress in cyanobacteria, Nostoc commune and some cyanobacteria with various tolerances to drying stress

Tolerance to and effects of the freezing stress in a desiccation-tolerant, terrestrial cyanobacterium, Nostoc commune, in cultivated strains of N. commune, and in desiccation-sensitive species, Synechocystis sp. PCC6803 and Fischerella muscicola, were studied by measuring their photosynthetic activities and fluorescence emission spectra. The results showed that a strain or species with higher desiccation tolerance was more tolerant to freezing stress than one with lower desiccation tolerance, which is consistent with the idea that tolerance to freezing stress is related to resistance to drying stress. Under freezing conditions, light energy absorbed by photosystem (PS) II complexes was dissipated to heat energy in N. commune, which may protect the cells from photoinactivation. N. commune encountered cellular dehydration due to ice formation outside the cell under freezing conditions. But NMR data showed that relatively high amounts of water still remained in a liquid state inside the cells at -36_C when N. commune colonies were fully wetted before freezing. High PSI activities measured by P700 photooxidation also support the result that non-freezing water remains within the cells. Besides, 5% methanol enhanced the resistance to freezing stress in the sensitive species. This effect seems to be related to maintenance of the PSI activity and pigment-protein complexes in their functional forms by methanol

Ycf12 is a core subunit in the photosystem II complex

AbstractThe latest crystallographic model of the cyanobacterial photosystem II (PS II) core complex added one transmembrane low molecular weight (LMW) component to the previous model, suggesting the presence of an unknown transmembrane LMW component in PS II. We have investigated the polypeptide composition in highly purified intact PS II core complexes from Thermosynechococcus elongatus, the species which yielded the PS II crystallographic models described above, to identify the unknown component. Using an electrophoresis system specialized for separation of LMW hydrophobic proteins, a novel protein of ∼5 kDa was identified as a PS II component. Its N-terminal amino acid sequence was identical to that of Ycf12. The corresponding gene is known as one of the ycf (hypothetical chloroplast reading frame) genes, ycf12, and is widely conserved in chloroplast and cyanobacterial genomes. Nonetheless, the localization and function of the gene product have never been assigned. Our finding shows, for the first time, that ycf12 is actually expressed as a component of the PS II complex in the cell, revealing that a previously unidentified transmembrane protein exists in the PS II core complex

Comparative analysis of photosynthetic properties in ice algae and phytoplankton inhabiting Franklin Bay, the Canadian Arctic, with those in mesophilic diatoms during CASES 03-04

Psychrophilic phytoplankton and ice algae were collected in Franklin Bay, the Canadian Arctic, in late May 2004, and the photosynthetic properties were measured at 4°C using a pulse amplitude modulation fluorometer (Phyto-PAM). Rapid light curve measurements allowed for the assessment of the photosynthetic efficiency (α), maximal electron transport rate (rETRmax), and minimum saturating irradiance (Ek) in the samples. The values of α in phytoplankton (0.63-0.68) were much larger than those in ice algae (0.10-0.51), and the values of rETRmax in phytoplankton (4.6-6.7) were relatively larger than those in ice algae (1.8-4.3). However, Ek showed similar values in both samples and were around 10μmol photonsm^・s^. These values were systematically compared with those obtained from mesophilic marine diatoms (a centric diatom, Chaetoceros gracilis, and a pennate diatom, Phaeodactylum tricornutum) grown under various irradiances in the laboratory. The highly shade-adapted features of ice algae and phytoplankton were disclosed through this comparative analysis. It was also found that the non-photochemical quenching was much higher in psychrophilic samples than in mesophilic diatoms grown under moderate irradiance. Furthermore, in ice algae and phytoplankton, the decrease in rETR at high irradiances was prominent, showing that they were highly susceptible to photoinhibition. Our comparative analysis using psychrophilic phytoplankton, ice algae and two strains of mesophilic diatoms also revealed that the dependency on the xanthophyll cycle for the protection mechanisms of photosystems were remarkably different between the groups, indicating that the acclimation strategies to growth irradiances were variable between species. Such variable acclimation strategies could be one of the forces that results in a diverse algal flora that enables this region around Franklin Bay to be a productive area, even though the psychrophilic phytoplankton and ice algae are highly shade-adapted