Effect of monochromatic UV-B radiation on electron transfer reactions of Photosystem II.

The adverse effect of low intensity, small band UV-B irradiation (lambda = 305 +/- 5 nm, I = 300 mW m(-2)) on PS II has been studied by comparative measurements of laser flash-induced changes of the absorption at 325 nm, DeltaA(325)(t), as an indicator of redox changes in Q(A), and of the relative fluorescence quantum yield, F(t)/F(o), in PS II membrane fragments. The properties of untreated control were compared with those of samples where the oxygen evolution rate under illumination with continuous saturating light was inhibited by up to 95%. The following results were obtained: a) the detectable initial amplitude (at a time resolution of 30 mus) of the 325 nm absorption changes, DeltaA(325), remained virtually invariant whereas the relaxation kinetics exhibit significant changes, b) the 300 mus kinetics of DeltaA(325) dominating the relaxation in UV-B treated samples was largely replaced by a 1.3 ms kinetics after addition of MnCl(2), c) the extent of the flash induced rise of the relative fluorescence quantum yield was severely diminished in UV-B treated PS II membrane fragments but the relaxation kinetics remain virtually unaffected. Based on these results the water oxidizing complex (WOC) is inferred to be the primary target of UV-B impairment of PS II while the formation of the 'stable' radical pair P680(+*)Q(A) (-) (*) is almost invariant to this UV-B treatment.

Analysis of the reaction coordinate of photosynthetic water oxidation by kinetic measurements of 355 nm absorption changes at different temperatures in photosystem II preparations suspended in either H2O or D2O.

Flash-induced absorption changes at 355 nm were measured at different temperatures within the range of 2 degrees C S2) = 14 kJ/mol, EA(S2-->S3) = 35 kJ/mol, and EA(S3-->-->S0 + O2) = 21 kJ/mol for theta > 11 degrees C, 67 kJ/mol for theta < 11 degrees C in PS II core complexes dissolved in H2O; (b) replacement of exchangeable protons by deuterons causes only minor changes ( S2, S2 --> S3, and S3 -->--> S0 + O2, respectively. The corresponding values of PS II membrane fragments are 1.3, 1.3, and 1. 4. Based on these results and corresponding EA data reported in the literature for PS II membrane fragments from spinach [Renger, G., & Hanssum, B. (1992) FEBS Lett. 299, 28-32] and PS II particles from the thermophilic cyanobacterium Synechococcus vulcanus Copeland [Koike, H., Hanssum, B., Inoue, Y., & Renger, G. (1987) Biochim. Biophys. Acta 893, 524-533], the reaction coordinate of the redox sequence in the WOC is inferred to be almost invariant to the evolutionary development from cyanobacteria to higher plants. Furthermore, the rather high activation energy of the S2 --> S3 transition provides evidence for a significant structural change coupled with this reaction. Implications for the mechanism of photosynthetic water oxidation are discussed.

Effects of hydrogen/deuterium exchange on photosynthetic water cleavage in PS II core complexes from spinach.

H/D isotope exchange effects on P680+. reduction by Yz and electron abstraction from the water oxidizing complex (WOC) in redox state S3 by YZOX were analyzed in PS II core complexes from spinach by measurements of laser flash induced absorption changes at 820 nm and 355 nm. The results obtained reveal: (1) the rate of Yz oxidation by P680+. is almost independent of the substitution of exchangeable protons by deuterons; and (2) the reaction between YZOX and the WOC in S3 exhibits a kinetic H/D isotope exchange effect of similar magnitude as that recently observed in PS II membrane fragments [Renger, G., Bittner, T. and Messinger, J. (1994) Biochem. Soc. Trans. 22, 318-322]. Based on these results it is inferred that photosynthetic dioxygen formation comprises the cleavage of at least one hydrogen bond.

Reconstitution of the endogenous plastoquinone pool in photosystem II (PS II) membrane fragments, inside-out-vesicles, and PS II core complexes from spinach.

The possibility of reconstituting a functionally competent endogenous plastoquinone pool in photosystem II (PS II) membrane fragments, inside-out-vesicles (ISO-vesicles), and PS II core complexes was analyzed by measuring (i) the characteristic period four oscillation of the oxygen yield due to excitation of dark-adapted samples with a train of short flashes and (ii) laser flash-induced transients of the relative quantum yield of chlorophyll fluorescence. The data obtained revealed that (a) an endogenous pool capacity comparable to that of intact thylakoids can be restored in PS II membrane fragments and ISO-vesicles by a sonication treatment using native plastoquinone-9, (b) a more pronounced oxygen oscillation pattern arises in PS II core complexes after application of the same reconstitution procedure, (c) the extent of the endogenous pool restoration at a ratio of 15 quinone molecules per PS II in the reconstitution assay strongly depends on the nature of the quinone molecule [maximum effects can be only achieved with PQ-9, while at the same concentration ubiquinone-45 (UQ-9) is almost inefficient], and (d) a sonication step is required for stable insertion of PQ-9 into PS II preparations. Measurements of the reconstruction degree as a function of the structure of different quinones with selected properties lead to the conclusion that specific binding domains exist in PS II in addition to the QB site. These domains exhibit a surprisingly high specificity for the type of quinone that can be bound. On the basis of a comparison of the results obtained, the structure of the quinone head group seems to be more important than the large hydrophobic side chain and/or the general lipophilicity of the compound.

Investigations of antithrombin III-activity in patients after myocardial infarction and a long-term coumarin therapy.

In 40 M.I. patients with long-term anticoagulant treatment, (Falithrom), the AT III-activity was determined at an interval of three years by means of Chromozym TH. We have found a mean AT III-value in the first testing period of 79.67 (+/- 14.16) per cent and in the second assessment of 82.5 (+/- 10.42) per cent. The difference is not significant. However, we were unable to confirm the comparatively marked increase AT III for dicoumarol treatment found by Roka and Bleyl. In acute M.I.-patients was demonstrated a decreased AT III-activity in the first 3-4 days and a normalisation tendency in the next 10-14 days. Our values of the mean AT III-activity were in the lower normal range for patients with long-term coumarin therapy. In dead patients (average age 70 years) there is a trend of a risk to an untimely death in the presence of pathologic AT III-activity (despite a good anticoagulation of an individual mean quick test from greater than or equal to 0.20 to less than or equal to 0.30) or a bad anticoagulation (mean individual quick tests greater than or equal to 0.30 to 0.35), but a normal AT III-activity. The three dimensional analysis was not significant.

A rapid quantitative method based on motility of bull sperm cells for in vitro toxicity testing of biomaterials.

A quantitative method for in vitro toxicity testing of biomaterials, based on measurements of time-dependent changes of bull sperm motility, is described. In comparison to the haemolytic and toxic effects of biomaterials such as polyurethanes, poly(vinyl chloride) tubes and bioglass ceramics on erythrocytes and the proliferation rate of human embryonic lung fibroblasts, this method is shown to be more sensitive. The simplicity, rapidity and reproducibility of the test under application of genetically identical cells are advantages that make it suitable for screening large numbers of samples. The quantification of test results allows inter-laboratory comparison.