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G H Schmid

Publications and source records attributed to G H Schmid.

At least 19 recordsLinked to original sources
PubMed2001

Heterogeneity of the mechanism of water splitting in photosystem II.

We measured the temperature dependence of oxygen evolution in thylakoids from tobacco using mass spectrometry and high resolution polarography. We determined the initial S-state distribution and the efficiency of the transition between these states including the probability of the O(2) yield through a fast mode. We observed discontinuous changes of the parameters at the temperatures 11 degrees C, 15 degrees C and 21 degrees C. Due to the mass spectroscopy data we think that the irregularity observed at 11 degrees C is due to conformational changes within the water catalytic site. We show that the different contributions of the slow and fast modes of oxygen evolution and of the water molecule exchange are correlated and that their behavior can be explained in terms of the H(2)O accessibility to the water splitting enzyme.

Mass Spectrometry↗
PubMed2001

An estimation of the size of the water cluster present at the cleavage site of the water splitting enzyme.

In time-dependent measurements of oxygen evolution in tobacco thylakoid membranes we varied the fraction of H(2)(18)O and the temperature and measured water splitting as (18)O(2), (16)O(18)O, and (16)O(2) by mass spectrometry. We show that the approach to the equilibrium of the system after H(2)(18)O addition can be very well understood in terms of the diffusion of water molecules. The equilibrium states of (16)O(2), (16)O(18)O, and (18)O(2) evolution differ from the theoretical binomial distributions, which are expected under the prerequisite of ideal mixing of the water molecules and that of the chemical equivalence of H(2)(18)O and H(2)(16)O for an infinite cluster. The presence of this deviation means that there is a typical size of water clusters having access to cleavage by the water splitting enzyme. We estimated that this cluster contains about 12+/-2 water molecules.

Algorithms↗
PubMed2000

Phosphatidylglycerol is involved in the dimerization of photosystem II.

Photosystem II core dimers (450 kDa) and monomers (230 kDa) consisting of CP47, CP43, the D1 and D2 proteins, the extrinsic 33-kDa subunit, and the low molecular weight polypeptides PsbE, PsbF, PsbH, PsbI, PsbK, PsbL, PsbTc, and PsbW were isolated by sucrose density gradient centrifugation. The photosystem II core dimers were treated with phospholipase A2 (PL-A2), which cuts phosphatidylglycerol (PG) and phosphatidylcholine molecules at the sn-2 position. The PL-A2-treated dimers dissociated into two core monomers and further, yielding a CP47-D1-D2 subcomplex and CP43. Thin layer chromatography showed that photosystem II dimers contained four times more PG than their monomeric counterparts but with similar levels of phosphatidylcholine. Consistent with this was the finding that, compared with monomers, the dimers contained a higher level of trans-hexadecanoic fatty acid (C16:1Delta3tr), which is specific to PG of the thylakoid membrane. Moreover, treatment of dimers with PL-A2 increased the free level of this fatty acid specific to PG compared with untreated dimers. Further evidence that PG is involved in stabilizing the dimeric state of photosystem II comes from reconstitution experiments. Using size exclusion chromatography, it was shown that PG containing C16:1Delta3tr, but not other lipid classes, induced significant dimerization of isolated photosystem II monomers. Moreover, this dimerization was observed by electron crystallography when monomers were reconstituted into thylakoid lipids containing PG. The unit cell parameters, p2 symmetry axis, and projection map of the reconstituted dimer was similar to that observed for two-dimensional crystals of the native dimer.

Chromatography, High Pressure Liquid↗
PubMed2000

Cooperative binding of oxygen to the water-splitting enzyme in the filamentous cyanobacterium Oscillatoria chalybea.

In the filamentous cyanobacterium Oscillatoria chalybea photolysis of water does not take place in the complete absence of oxygen. A catalytic oxygen partial pressure of 15x10(-6) Torr has to be present for effective water splitting to occur. By means of mass spectrometry we measured the photosynthetic oxygen evolution in the presence of H(2)(18)O in dependence on the oxygen partial pressure of the atmosphere and analysed the liberations of (16)O(2), (16)O(18)O and (18)O(2) simultaneously. The observed dependences of the light-induced oxygen evolution on bound oxygen yield sigmoidal curves. Hill coefficient values of 3.0, 3.1 and 3.2, respectively, suggest that the binding is cooperative and that four molecules of oxygen have to be bound per chain to the oxygen evolving complex. Oxygen seems to prime the water-splitting reaction by redox steering of the S-state system, putting it in the dark into the condition from which water splitting can start. It appears that in O. chalybea an interaction of oxygen with S(0) and S(1) leads to S(2) and S(3), thus yielding the typical oxygen evolution pattern in which even after extensive dark adaptation substantial amounts of Y(1) and Y(2) are found. The interacting oxygen is apparently reduced to hydrogen peroxide. Mass spectrometry permits to distinguish this highly specific oxygen requirement from the interaction of bulk atmospheric oxygen with the oxygen evolving complex of the cyanobacterium. This interaction leads to the formation H(2)O(2) which is decomposed under O(2) evolution in the light. The dependence on oxygen-partial pressure and temperature is analysed. Structural peculiarities of the cyanobacterial reaction centre of photosystem II referring to the extrinsic peptides might play a role.

Cyanobacteria↗
PubMed2000

Localization of NADPH-protochlorophyllide reductase in plastids of barley at different greening stages.

The localization of protochorophyllide (Pchlide) and of NADPH-protochlorophyllide oxidoreductase (POR, EC 1.6.99.1) within (etio)chloroplasts has been investigated at selected stages of greening of barley seedlings. Pchlide pigment and POR protein contents were evaluated in different plastid membrane fractions by fluorescence spectroscopy and immunoblot analysis using a monospecific polyclonal antibody raised against the purified enzyme. Fluorescence analysis showed the presence of Pchlide in both the envelope and thylakoid membranes. During greening, the Pchlide content, expressed on a total protein basis, decreased in thylakoid membranes, whereas it increased in the envelope membranes. POR proteins were detected mainly in thylakoid membranes at early greening stages. In contrast, the weak amount of POR proteins was associated more specifically with envelope membranes of mature chloroplasts. Whatever the greening stage, thylakoid-bound Pchlide and POR proteins were more abundant in the thylakoid regions which remained unsolubilized after mild Triton treatment used as standard procedure to prepare PS II particles. This suggests the preferential association of Pchlide and POR to the appressed regions of thylakoids.

Journal Article↗
PubMed2000

State of the lipid and fatty acid composition in chloroplasts of Nicotiana tabacum under the influence of an increased CO2 partial pressure of 700 p.p.m.

We analysed chloroplast lipids of Nicotiana tabacum var. John William's Broadleaf, cultivated under an increased PCO(2) of 700 p.p.m. Glycolipids and phospholipids remain constant under these conditions, whereas the carotenoid content undergoes a quantitative change. The saturation degree of fatty acids increases due to an increase in palmitic acid and decreases in hexadecatrienoic acid and linolenic acid.

Carbon Dioxide↗
PubMed1996

Nucleotide sequence of the nar beta gene encoding assimilatory nitrate reductase from the cyanobacterium Oscillatoria chalybea.

The nucleotide sequence of the structural gene of nitrate reductase (n ar beta) has been determined from the filamentous, non-heterocystous cyanobacterium Oscillatoria chalybea. The nar beta gene encodes a protein of 737 amino acid residues, which shows 61% identity to nitrate reductase of the unicellular cyanobacterium Synechococcus sp. PCC 7942 and only weak homologies to different bacterial molybdoenzymes, such as nitrate reductases or formate dehydrogenases.

Alcaligenes↗
PubMed1979

Inhibition of photosynthetic electron transport in tobacco chloroplasts and thylakoids of the blue green alga Oscillatoria chalybea by an antiserum to synthetic zeaxanthin.

An antiserum to synthetic Zeaxanthin inhibits photosynthetic electron transport on the oxygen-evolving side of photosystem II in tobacco chloroplasts and thylakoids of the filamentous blue-green alga Oscillatoria chalybea. The inhibition site lies for both species between the site of electron donation of water or tetramethyl benzidine and that of diphenyl carbazide or manganese II ions. Typical photosystem I reactions are not impaired by the antiserum. The effect of the antiserum concerning the inhibition site is practically identical to that of the earlier described antiserum to violaxanthin. However, the degree of inhibition seems to be generally somewhat lower with the antiserum to Zeaxanthin, than with that to violaxanthin which hints at a lesser accessibility of zeaxanthin, in the tylakoid membrane in comparison to violaxanthin. In the course of these investigations new evidence was obtained that the oxygen-evolving side of the electron transport scheme is differently organized in Oscillatoria chalybea when compared to tobacco chloroplasts. Thus, the silicomolybdate reduction with water as the electron donor is sensitive to DCMU in these algae.

Carotenoids↗
PubMed1977

Photooxidation reactions of diphenylcarbazide and their DCMU-sensitivity in thylakoids of the blue-green alga Oscillatoria chalybea.

Thylakoids of Oscillatoria chalybea are able to split water. The Hill reaction of these thylakoids is sensitive to DCMU. Diphenylcarbazide can substitute for water as the electron donor to photosystem II with these fully functioning thylakoids. However, the diphenylcarbazide photooxidation is completely insensitive to 3-(3,4-dichlorophenyl)-N-N'-dimethyl urea (DCMU) at high diphenylcarbazide concentrations. In with Tris-treated Oscillatoria thylakoids the water splitting capacity is lost and diphenylcarbazide restores electron transport through photosystem II as occurs with higher plant chloroplasts. However, also these photoreactions are insensitive to DCMU. If diphenylcarbazide acts in Oscillatoria as an electron donor to photosystem II the result suggests that diphenylcarbazide feeds in its electrons behind the DCMU inhibition site. This in turn indicates that in Oscillatoria the site of inhibition of DCMU is on the donor side of photosystem II.

Chloroplasts↗
PubMed1977

Genetic characterization and high efficiency photosynthesis of an aurea mutant of tobacco.

A new tobacco (Nicotiana tabacum) aurea mutant was isolated from the progeny of a selfed variegated tobacco plant. The new mutant is termed Su/su var. Aurea. If the mutant is selfed, the seeds obtained give rise to four types of plants: green seedlings which correspond to the wild type; yellow-green seedlings which correspond to the earlier described Su/su; yellow seedlings which correspond to the new tobacco aurea mutant Su/su var. Aurea; and white lethal seedlings. The frequency ratio of the four phenotypes is 1:1:1:1. It appears that the mutation is due to two independent nuclear factors, su and aur, both of which have to be present in a heterozygous conditions, Su/su Aur/aur, to give rise to the new aurea phenotype. The aurea mutant Su/su var. Aurea has a reduced photosynthetic unit size which is approximately one-eighth of the wild type. Despite its chlorophyll deficiency, the plant grows well and exhibits maximal photosynthetic rates on a chlorophyll basis which are at least seven times higher than those of the green wild type provided the temperature and the light intensities are high enough. In contrast to the earlier described Su/su, the new mutant does not exhibit more photorespiration than the wild type. It appears that the factor aur causes either repression of photorespiration or an increase in the number of functioning photosynthetic units.

Journal Article↗
PubMed1976

Cyclic Photophosphorylation in the Mykotrophic Orhid Neottia nidus-avis.

The mykotrophic orchid Neottia nidus-avis (L.) Rich. is not able to evolve oxygen in the light. Plastid preparations from the lip (labellum) of the orchid perform a photosystem I-dependent photoreduction of methylviologen with the artificial electron donor couple 2,6-dichlorophenol indophenol ascorbate. Photosystem II reactions such as the ferricyanide Hill reaction or the photoreduction of 2,6-dichlorophenol indophenol with diphenylcarbazide as the electron donor are not functioning. The plastids exhibit phenazine methosulfate-mediated cyclic photophosphorylation. After infiltration with (32)P-labeled phosphate the labellum forms (32)P-ATP in the light. This rate of ATP formation is enhanced by additional infiltration of phenazine methosulfate prior to illumination. The brown color of the plant is caused by an absorption shift of carotenoids to longer wavelength. By comparison of absorption spectra with the fluorescence excitation spectra of plastid preparations and of the extracted pigments we show that no appreciable energy transfer from carotenoids to chlorophyll occurs.

Journal Article↗