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  • 11
    ISSN: 1573-5079
    Keywords: Photoinhibition ; Photosystem II ; quinone-iron complex ; electron paramagnetic resonance (EPR) ; thermoluminescence (TL)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosystem II particles were exposed to 800 W m−2 white light at 20 °C under anoxic conditions. The Fo level of fluorescence was considerably enhanced indicating formation of stable-reduced forms of the primary quinone electron acceptor, QA. The Fm level of fluorescence declined only a little. The g=1.9 and g=1.82 EPR forms characteristic of the bicarbonate-bound and bicarbonate-depleted semiquinone-iron complex, QA −Fe2+, respectively, exhibited differential sensitivity against photoinhibition. The large g=1.9 signal was rapidly diminished but the small g=1.82 signal decreased more slowly. The S2-state multiline signal, the oxygen evolution and photooxidation of the high potential form of cytochrome b-559 were inhibited approximately with the same kinetics as the g=1.9 signal. The low potential form of oxidized cytochrome b-559 and Signal IIslow arising from TyrD + decreased considerably slower than the g=1.9 semiquinone-iron signal. The high potential form of oxidized cytochrome b-559 was diminished faster than the low potential form. Photoinhibition of the g=1.9 and g=1.82 forms of QA was accompanied with the appearance and gradual saturation of the spin-polarized triplet signal of P 680. The amplitude of the radical signal from photoreducible pheophytin remained constant during the 3 hour illumination period. In the thermoluminescence glow curves of particles the Q band (S2QA − charge recombination) was almost completely abolished. To the contrary, the C band (TyrD +QA − charge recombination) increased a little upon illumination. The EPR and thermoluminescence observations suggest that the Photosystem II reaction centers can be classified into two groups with different susceptibility against photoinhibition.
    Type of Medium: Electronic Resource
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  • 12
    ISSN: 1573-5079
    Keywords: acetate metabolism ; ATP demand ; green alga ; photosystem stoichiometry ; redox control ; state transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of acetate metabolism on the light energy distribution between the two photosystems, on the PS II/PS I stoichiometry and on the expression of psbA and psbB and psaA genes was investigated in the green alga, Chlamydobotrys stellata during autotrophic (CO2), mixotrophic (CO2 plus acetate) and photoheterotrophic (only acetate) cultivation. It was observed that acetate assimilation in the glyoxylate cycle resulted in a large drop in the ATP content and a concomitant increase in the NADPH content of the cells. The combined effect of high NADPH concentration and linear electron transport brought about an over-reduction of the inter-photosystem electron transport components. The reduced state of the inter-photosystem components initiated a state 1/state 2 transition of LHC II and a decrease in the PS II/PS I ratio. The PS II/ PS I ratio was reduced because the synthesis of PS II reaction centers was repressed and that of the PS I reaction centers was slightly enhanced by acetate cultivation. The amount of PsbA and PsbB proteins of PS II and the abundance of psbA mRNA decreased. The abundance of PS I PsaA protein and psaAmRNA were only slightly increased. All of the acetate-induced effects were reversible when the cells were transferred back to an acetate-free medium. Our observations demonstrate that the expression of the PS II psbA and psbB and PS I psaA genes is regulated by the redox state of the inter-photosystem components at the transcriptional level. Experiments carried out in the presence of DBMIB which facilitates the reduction of plastoquinone pool indicate that the expression of genes encoding the components of PS II and PS I are controlled by the redox state of a component (cytochrome b/f complex) located behind the plastoquinone pool.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Advances in contraception 12 (1996), S. 241-241 
    ISSN: 1573-7195
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Journal of assisted reproduction and genetics 16 (1999), S. 35-40 
    ISSN: 1573-7330
    Keywords: creatine kinase ; male fertility ; unexplained ; maturity ; biochemical markers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Purpose: Our purpose was to measure sperm creatine phosphokinase (CK) activity, which reflects cytoplasmic retention in immature spermatozoa, in normospermic and oligozospermic Hungarian men. Methods: A study of 109 randomly selected men in a university-based andrology laboratory was done. Results: CK activity differed between normospermic and oligozospermic men (0.21 ± 0.02 vs. 1.19 ± 0.15 CK IU/10 8 sperm; n = 56 and n = 53; mean ± standard error of the mean, respectively). There was an inverse correlation between sperm concentration and CK activity (r = −0.70; n = 109). However, 28% of men in the range with less than 10 million sperm/ml had normal sperm CK activity (below the mean + 2 standard deviations of the group with greater than 30 × 10 6 sperm/ml), whereas 36% of men in the group with 20–30 million sperm/ml and 5% in the group with greater than 30 million sperm/ml had elevated CK activities, indicating that the incidence of mature and immature spermatozoa in specimens is independent from the sperm concentrations. Conclusions: The improved facility of sperm CK activity measurements, compared with sperm concentrations, in the assessment of sperm maturity was confirmed in a Hungarian population. The CK measurements aid the selection of the most efficient treatment for couples with male-factor or unexplained infertility, particularly when considering the options of intrauterine insemination, varicocelectomy followed by a waiting period, or ovulation workup/induction in wives of men who are oligozospermic but may have fertile sperm.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Science & education 5 (1996), S. 309-311 
    ISSN: 1573-1901
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General
    Notes: Abstract The present article is based on Zoltán Bay's ‘Old Education, New Teaching’ — an unpublished paper written for the XXVIIth National Meeting of Secondary School Physics Teachers (5–7th April, 1984 Veszprém, Hungary).
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Science & education 7 (1998), S. 313-316 
    ISSN: 1573-1901
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General
    Notes: Abstract This paper describes the first moon-radar echo experiment conducted by Zoltán Bay in Hungary in 1946, and makes some comment on Bay as a model for contemporary physics students.
    Type of Medium: Electronic Resource
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  • 17
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Following prolonged exercise, muscle force production is often impaired. One possible cause of this force deficit is impaired intracellular activation. We have used single skeletal muscle fibers from the lumbrical muscle of Xenopus laevis to study the effects of fatigue on excitation–contraction coupling. Fatigue was induced in 13 intact fibers. Five fibers recovered in normal Ringer only (fatigued-only fibers). The remaining eight fibers were subjected to a brief hypotonic treatment (F-H fibers) that is known to prolong the effects of fatigue. Intramembrane charge movement, changes in intracellular calcium concentration ([Ca2+]i) and force transients were measured in a single Vaseline gap chamber under voltage clamp. In F-H fibers, membrane capacitance was reduced. Confocal microscopy showed that this was not due to closure of the transverse tubules. The amount of normalized intramembrane charge was reduced from 21.0 ± 2.8 nC/μF (n = 10) in rested fibers to 12.2 ± 1.1 nC/μF in F-H fibers. However, the voltage dependence of intramembrane charge movement was unchanged. In F-H fibers, force production was virtually abolished. This was the consequence of the greatly reduced [Ca2+]i accompanying a depolarizing pulse. In recovering fatigued-only fibers, while the maximal available charge was not significantly smaller (18.3 ± 1.1 nC/μF), both calcium and force were reduced, albeit to a lesser extent than in F-H fibers. The data are consistent with a model where fatigue reduces the number of voltage sensors in the t-tubules and, in addition, alters the coupling between the remaining functional voltage sensors and the calcium channels of the sarcoplasmic reticulum.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Journal of muscle research and cell motility 9 (1988), S. 541-551 
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effect of the chaotropic cation guanidinium on tension generation was investigated in voltage-clamped intact and mechanically skinned muscle fibres of the frog. When sodium was replaced by guanidinium in the solution a 20-mV shift of the sigmoidal activation curve towards less negative potentials was recorded. A similar shift in the voltage dependence of mechanical inactivation did not occur. The plateau phase of contractures activated by long-lasting depolarizations was significantly shortened in the presence of 77.5mm guanidinium. In a second set of experiments, charge displacement currents were measured using the cut fibre preparation. Apparently, guanidinium had no effect on the voltage dependence of intramembrane charge movement. On the other hand, this cation caused a distinct increase in the amount of charge necessary to reach the contraction threshold at rheobase voltage from 12.4 nC ΜF−1 to 23.4 nC ΜF−1. Experiments on skinned fibres containing an operating sarcoplasmic reticulum demonstrated that 5mm guanidinium diminished caffeine-induced tension development and substantially delayed the onset of the contractile response. However, guanidinium did not impair calcium-induced tension development of the contractile apparatus. These results suggest that the inhibitory action of guanidinium on excitation-contraction coupling is due to a depression of calcium release from the sarcoplasmic reticulum.
    Type of Medium: Electronic Resource
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  • 19
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effects of low (10–100 μm) concentrations of tetracaine on intramembrane charge movement and on the rate of calcium release (Rrel) from the sarcoplasmic reticulum (SR) were studied in cut skeletal muscle fibres of the frog using the voltage clamp technique. The fibres were mounted in a single or double vaseline gap chamber to study the events near the contraction threshold or in a wide membrane potential range. Although the ‘hump’ component of charge movement (Qγ) was suppressed to some extent, the voltage dependence and the parameters of the Boltzmann distribution were not modified significantly at tetracaine concentrations below 50 μm. At 50 and 100 μm of tetracaine the midpoint voltage of the Boltzmann distribution was shifted to higher membrane potentials and the steepness was decreased. The total available charge remained the same at all concentrations tested. Using fura-2 to measure calcium transients at 100 μm tetracaine the threshold for calcium release was found to be significantly shifted to more positive membrane potentials. Tetracaine reversibly suppressed both the early inactivating peak and the steady-level of Rrel but the concentration dependence of these effects was markedly different. The inactivating component of calcium release was decreased with a Hill coefficient of approximately 1 and half effective concentration of 11.8 μm while the steady-level was decreased with a Hill coefficient of greater than 2 and a half effective concentration of 47.0 μm. These results favour two sites of action where tetracaine would suppress the calcium release from the SR.
    Type of Medium: Electronic Resource
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  • 20
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The regulation by calcium of the ryanodine receptor/SR calcium release channel (RyR) from rat skeletal muscle was studied under isolated conditions and in situ. RyRs were either solubilized and incorporated into lipid bilayers or single fibres were mounted into a Vaseline gap voltage clamp. Single channel data were compared to parameters determined from the calculated calcium release flux. With K+ (250 mM) being the charge carrier the single channel conductance was 529 pS at 50 μM Ca2+ cis and trans, and decreased with increasing cis [Ca2+]. Open probability showed a bell shaped calcium dependence revealing an activatory and an inhibitory Ca2+ binding site (Hill coefficients of 1.18 and 1.28, respectively) with half activatory and inhibitory concentrations of 9.4 and 298 μM. The parameters of the inhibitory site agreed with the calcium dependence of channel inactivation deduced from the decline in SR calcium release in isolated fibres. Mean open time showed slight [Ca2+] dependence following a single exponential at every Ca2+ concentration tested. Closed time histograms, at high [Ca2+], were fitted with three exponentials, from which the longest was calcium independent, and resembled the recovery time constant of SR inactivation (115 ± 15 ms) obtained in isolated fibres. The data are in agreement with a model where calcium binding to the inhibitory site on RyR would be responsible for the calcium dependent inactivation in situ.
    Type of Medium: Electronic Resource
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