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K Sauer

Publications and source records attributed to K Sauer.

At least 109 records · Page 6Linked to original sources
PubMed1976

A flash photolysis ESR study of photosystem II signal IIvf, the physiological donor to P-680+.

In flash-illuminated, oxygen-evolving spinach chloroplasts and green algae, a free radical transient has been observed with spectral parameters similar to those of Signal II (g approximately 2.0045, deltaHpp approximately 19G). However, in contrast with ESR Signal II, the transient radical does not readily saturate even at microwave power levels of 200 mW. This species is formed most efficiently with "red" illumination (lambda less than 680 nm) and occurs stoichiometrically in a 1:1 ratio with P-700+. The Photosystem II transient is formed in less than 100 mus and decays via first-order kinetics with a halftime of 400-900 mus. Additionally, the t1/2 for radical decay is temperature independent between 20 and 4 degrees C; however, below 4 degrees C the transient signal exhibits Arrhenius behavior with an activation energy of approx. 10 kcal-mol-1. Inhibition of electron transport through Photosystem II by o-phenanthroline, 3-(3,4-dichlorophenyl)-1,1-dimethylurea or reduced 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone suppresses the formation of the light-induced transient. At low concentrations (0.2 mM), 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone partially inhibits the free radical formation, however, the decay kinetics are unaltered. High concentrations of 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (1-5 mM) restore both the transient signal and electron flow through Photosystem II. These findings suggest that this "quinoidal" type ESR transient functions as the physiological donor to the oxidized reaction center chlorophyll, P-680+.

Chlorella↗
PubMed1975

Two electron donation sites for exogenous reductants in chloroplast photosystem II.

Two sites are distinguished for the oxidation of exogenous donors by Photosystem II in non-oxygen evolving chloroplasts. In the presence of lipophilic donors (e.g. phenylenediamine, benzidine, diphenylcarbazide), the rate for Signal IIf rereduction following a flash increases as the concentration of exogenous reductant increases. There is a decrease (20-40%) in Signal IIf magnitude accompanying donor addition at low (smaller than 10(-%) M) concentrations, but the extent of the decrease does not change further with increasing donor concentrations. Complementary polarographic experiments monitoring donor (phenylenediamine) oxidation show an increase in oxidation rate with increasing donor concentration. In the presence of the hydrophilic donor, Mn-2+, the Signal IIf decay halftime remains constant with increasing Mn-2+ concentration. However, the flash-induced Signal IIf magnitude pregressively decreases with increasing Mn-2+ concentration. These results are interpreted in terms of two competing paths for the reduction of P680+. In one path P680+ reduction is accompanied by the appearance of Signal IIf, and lipophilic donors subsequently rereduce the Signal IIf species in a series reaction. This reduction follows pseudo-first order kinetics as a function of donor concentration. In the second path Mn-2+ reduces P680+ in a parallel reaction that competes with the formation of the Signal IIf species. This results in a decrease in the magnitude of Signal IIf, but no change in its decay time.

Ascorbic Acid↗
PubMed1975

Flash kinetics and light intensity dependence of oxygen evolution in the blue-green alga Anacystis nidulans.

Patterns of oxygen evolution in flashing light for the glue-green alga Anacystis nidulans are compared with those for broken spinach chloroplasts and whole cells of the green alga Chlorella pyrenoidosa. The oscillations of oxygen yield with flash number that occur in both Anacystis and Chlorella, display a greater degree of damping than do those of isolated spinach chloroplasts. The increase in damping results from a two- to threefold increase in the fraction (alpha) of reaction centers "missed" by a flash. The increase in alpha cannot be explained by non-saturing flash intensities or by the dark reduction of the oxidized intermediates formed by the flash. Anaerobic conditions markedly increase alpha in Anacystis and Chlorella but have no effect on alpha in broken spinach chloroplasts. The results signify that the mechanism of charge separation and water oxidation involved in all three orgainsms is the same, but that the pool of secondary electron acceptors between Photosystem II and Photosystem I is more reduced in the dark, in the algal cells, than in the isolated spinach chloroplasts. Oxygen evolution in flashing light for Anacystis and Chlorella show light saturation curves for the oxygen yield of the third flash (Y3) that differ markedly from those of the steady-state flashes(YS). In experiments in which all flashes are uniformly attenuated, Y3 requires nearly twice as much light as YS to reach half-saturation. Under these conditions Y3 has a sigmoidal dependence on intensity, while that of YS is hyperbolic. These differences depend on the number of flashes attenuated. When any one of the first three flashes is attenuated, the variation of Y3 with intensity resembles that of YS. When two of the first three flashes are attenuated, Y3 is intermediate in shape between the two extremes. A quantitative interpretation of these results based on the model of Kok et al. (Kik, B., Forbush, B.and McGloin, M. (1970) Photochem. Photobiol. 14, 307-321) fits the experimental data.

Chlorella↗
PubMed1975

Kinetic study of oxygen evolution parameters in Triswashed, reactivated chloroplasts.

Tris-washed chloroplasts which have lost the ability to evolve oxygen can be reactivated by the procedure of Yamashita T., Tsuji, J. and Tomita G. (1971) Plant Cell Physiol. 12, 117-126) [7] to give 100 percent of the rate of control chloroplasts in continuous illumination. Furthermore, in flashing light the reactivated chloroplasts exhibit oxygen-yield oscillations of period four that are characteristic of the control. Similar kinetic parameters for intermediate steps in the water-splitting process are observed for the two preparations. We conclude that the reactivation procedure restores the native oxygen evolution mechanism to Tris-washed chloroplasts. A relatively rapid and reversible (0.5 s decay) light-induced component of EPR Signal II is observed upon inhibition of O2 evolution by Tris washing (Babcock G. T. and Sauer, K. (1975) Biochim. Biophys. Acta 376, 315-328) [10]. Reactivated chloroplasts are similar to untreated chloroplasts in that this Signal IItransient is not observed. Manganese, which is released by Tris treatment to the interior of the thylakoid membrane in an EPR-detectable state, is returned to an EPR-undetectable state by reactivation. The reactivation procedure does not require light to restore O2 evolution and EDTA has no effect on the extent of reactivation. These results are discussed in terms of possible mechanisms for manganese incorporation into photosynthetic membranes.

Cell Membrane↗
PubMed1975

Magnetic circular dichroism studies on microsomal aryl hydrocarbon hydroxylase: comparison with cytochrome b-5 and cytochrome P-450-cam.

Magnetic circular dichroism spectra are reported for the visible and near ultraviolet spectral regions of liver microsomes from dimethylbenzanthracene-treated rats. The sequential addition of NADH, dithionite, and carbon monoxide enables us to determine contributions to the magnetic circular dichroism by cytochromes b-5 and P-450, which dominate the spectra. The magnetic circular dichroism of the microsomal preparation is compared with that of purified oxidized and reduced cytochrome -b-5 from pig liver and with the camphor-complexed and camphor-free oxidized, reduced, and reduced carbonmonoxy cytochrome P-450-cam from Pseudomonas putida. The magnetic circular dichroism spectra of the membrane bound cytochrome -b-5 are similar to those of the purified protein, indicating that little or no alteration in the environment of the heme occurs during the isolation procedure. The soluble bacterial cytochrome P-450 also appears to be a suitable model for microsomal P-450, although differences in the magnetic circular dichroism intensity are observed for the two enzymes. No effect of dimethylbenzanthracene on the magnetic circular dichroism spectra of induced compared to control rat microsomes could be observed.

Animals↗
PubMed1975

A rapid, light-induced transient in electron paramagnetic resonance signal II activated upon inhibition of photosynthetic oxygen evolution.

A rapid, light-induced reversible component in Signal II is observed upon inhibition of oxygen evolution in broken spinach chloroplasts. The inhibitory treatments used include Tris washing, heat, treatment with chaotropic agents, and aging. This new Signal II component is in a 1 : 1 ratio with Signal I (P700). Its formation corresponds to a light-induced oxidation which occurs in less than 500 mus. The subsequent decay of the radical results from a reduction which occurs more rapidly as this free radical component is complete following a single 10-mus flash, and it occurs with a quantum efficiency similar to that observed for Signal I formation. Red light is more effective than far-red light in the generation of this species, and, in preilluminated chloroplasts, 3-(3,4-dichlorophenyl)-1,1-dimethylurea blocks its formation. Inhibition studies show that the decline in oxygen evolution parallels the activation of this Signal II component. These results are interpreted in terms of a model in which two pathways, one involving water, the other involving the rapid Signal II component, compete for oxidizing equivalents generated by Photosystem II. In broken chloroplasts this Signal II pathway is deactivated and water is the principal electron donor. However, upon inhibition of oxygen evolution, the Signal II pathway is activated.

Chloroplasts↗
PubMed1975

The rapid component of electron paramagnetic resonance signal II: a candidate for the physiological donor to photosystem II in spinach chloroplasts.

Rapid light-induced transients in EPR Signal IIf (F-+) are observed in 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-treated, Tris-washed chloroplasts until the state F P680 Q minus is reached. In the absence of exogenous redox mediators several flashes are required to saturate this photoinactive state. However, the Signal IIf transient is observed on only the first flash following DCMU addition if an efficient donor to Signal IIf, phenylenediamine or hydroquinone, is present. Complementary polarographic measurements show that under these conditions oxidized phenylenediamine is produced only on the first flash of a series. The DCMU inhibition of Signal IIf can be completely relieved by oxidative titration of a one-electron reductant with E'Os.o equals to + 480 mV. At high reduction potentials the decay time of Signal IIf is constant at about 300 ms, whereas in the absence of DCMU the decay time is longer and increases with increasing reduction potential. A model is proposed in which Q minus, the reduced Photosystem II primary acceptor, and D, a one-electron 480 mV donor endogenous to the chloroplast suspension, compete in the reduction of Signal IIf (F-+). At high potentials D is oxidized in the dark, and the (Q-+F-+) back reaction regenerates the photoactive F P680 Q state. The electrochemical and kinetic evidence is consistent with the hypothesis that the Signal IIf species, F, is identical with Z, the physiological donor to P680.

Chloroplasts↗
PubMed1975

Chemically induced dynamic electron polarization in chloroplasts at room temperature: evidence for triplet state participation in photosynthesis.

A transient electron paramagnetic resonance emission is observed after flash excitation of chloroplasts at room temperature. The spectrum of the emission signal is centered at g = 2.0037 and has a linewidth deltaHpp = 4G (4 X 10(-4) tesla). Inhibitor studies and chemical oxidation indicate that the signal is associated with Photosystem I, but the spectrum and kinetics indicate that it is neither P700 nor an iron-sulfur protein. The emission signal rises with the 2-musec time response of the instrument, and decays during the actinic flash. The emission signal is produced on only the first of a pair of strong flashes separated by 100 musec, indicating that the precursor has not been regenerated in that time. The results are discussed with reference to the two currently accepted mechanisms for chemically induced dynamic electron polarization: the radical pair and the photochemical triplet. For several reasons the photochemical triplet mechanism is the more attractive of the two. It is suggested that at room temperature the primary photochemistry of photosystem I proceeds via a triplet state of chlorophyll, and that the species giving rise to the emission signal is the primary electron acceptor of Photosystem I.

2,6-Dichloroindophenol↗