[Establishment of an animal model of Sparganum mansoni infection and study on therapeutic methods II Establishment of a mouse model of sparganosis mansoni via oral administration of procercoids].

OBJECTIVE: To establish an animal model of sparganosis mansoni through oral administration of Cyclops infected with procercoids. METHODS: Domestic cats were infected with Sparganum mansoni under laboratory conditions, and fresh cat stool samples were collected, washed in dechlorinated water, and filtered. Spirometra mansoni eggs were collected and prepared into suspensions. Twenty C57BL/6j mice were randomly divided into the experimental group (n = 15) and the control group (n = 5). Wild Cyclops were infected with Spirometra mansoni coracidia to allow 3 to 5 procercoids in each Cyclop. Then, each mouse in the experimental group was given 15 Cyclops infected with procercoids by gavage, while mice in the control group were orally administered with the same volume of dechlorinated water. All mice were sacrificed after 5 months, and dissected, and suspicious Sparganum mansoni worms were collected. The serum specific IgG antibody against Sparganum mansoni was measured in mice using enzyme-linked immunosorbent assay (ELISA). Genomic DNA was isolated from suspicious Sparganum mansoni worms, and the specific Sparganum mansoni cytochrome oxidase I (COI) gene was amplified using PCR assay. RESULTS: Among the 15 mice in the experimental group, six were positive for the serum specific IgG antibody against Sparganum mansoni, and milky white worms were found and collected from the subcutaneous regions of 4 out of 6 mice. Only one worm was detected in each mouse, and the worm morphology was similar to Sparganum mansoni. Capillary electrophoresis of the PCR amplification products of COI gene presented a specific band with 151 bp in size, and sequencing analysis revealed 100% homology with Sparganum mansoni. CONCLUSIONS: A mouse model of sparganosis mansoni is successfully created through oral administration of Cyclops infected with Spirometra mansoni procercoids.

Quasi-isentropic compression of LiH above 400 GPa using magnetocumulative generator.

The knowledge of high-pressure behavior of LiH is significant for the validation of fundamental theoretical models and applications in thermonuclear materials and potential energy supplies. The compressibility of 7LiH under isentropic compression at high pressure was investigated experimentally and theoretically. The experimental technique for quasi-isentropic compression with low-density materials was developed using the magnetocumulative generator CJ-100 and x-ray flash radiography. The x-ray images and extracted interface of the sample target in dynamic flash radiography experiments were obtained. According to each interface size of the target both before and after compression, the compression ratio of 7LiH and reference material aluminum was obtained. The density of the reference and using its known isentropic curve provide the pressure in the reference. The pressure in 7LiH was deduced from the pressure in the reference and using the calculated gradient correction factor. The quasi-isentropic data point at 438 GPa was obtained experimentally. A semiempirical three-term complete equation of state was constructed and validated for 7LiH using the theory of Mie-Grüneisen-Debye with experimental data from the literature. The quasi-isentrope data point is reasonably consistent with the theoretical results. The quasi-isentropic experimental techniques and results broaden the existing research scope and are practical and helpful to further validate theoretical models in the future.

[Clinical and prognosis analysis of children with kidney retransplantation].

Objective: To analyze the clinical and prognosis of children with kidney retransplantation. Methods: Clinical data of 11 children who underwent kidney retransplantation from January 2011 to December 2020 in Department of Nephrology, Children's Hospital of Fudan University were retrospectilely analyzed. The clinical data including demographic parameters, primary diagnosis, characteristics in the follow-up of renal allograft were analyzed. Results: Totally 11 cases received secondary renal transplantation (male 6, female 5). They were initially diagnosed with chronic kidney disease at the age of 11.9 (7.4, 13.3) years. The median duration of dialysis was 22.1 (3.5, 36.5) months. In the first transplantation, recipient age was 13.9 (11.1, 15.2) years. Ten cases received donation from cardiac death donor (DCD) (9 cases received donors aged less than one year, 5 of them received whole kidney transplantation and one case received donor aged one to three years) and 1 case with living-related donor. Ten graft failures occurred within 1 month after renal transplantation and the other one occurred at the fifth month after transplantation. The causes included vascular factors (9 cases), rejection (1 case) and primary non-function (1 case). In the second transplantation, recipient age was 14.7 (11.7, 16.2) years. All the 11 children received dialysis (7 with PD and 4 with HD) and successfully completed the second transplantation. The median time between the two transplants was 210 (16, 1 041) days. Donors were all DCD donors from 3 years of age or older. The mean follow-up duration was (42±15) months. The estimated glomerular filtration rate was (85±34)ml/(min·1.73 m2) when the last investigation after kidney retransplantation with the kidney and patient all survived. Conclusions: Kidney retransplantation may have better prognosis in children. Dialysis transition during waiting period and DCD donor from 3 years of age or older can effectively ensure the success of kidney retransplantation.

An ultrasensitive heart-failure BNP biosensor using B/N co-doped graphene oxide gel FET.

Heart failure (HF) is the number one cause of death in the world. B-type natriuretic peptide (BNP) is a recognized biomarker for HF and can be used for early detection. Field effect transistor (FET) biosensors have the ability to sense BNP in much shorter times than conventional clinical studies. The lowest limit of detection (LOD) of state-of-the-art HF FET biosensors is 100 fM and detection ranges are short, being less than 4 orders of magnitude. In this work, a B/N co-doped graphene oxide (GO) gel (BN-GO) was used as the channel material in an FET biosensor targeting BNP. The sensor was able to sense BNP in as little as 2 min, with an LOD as low as 10 aM and a wide linear detection range of 10 aM-1 µM, stretching over 11 orders of magnitude. The biosensor showed great selectivity and minimal response towards K+ and OH- ions and the human epidermal growth factor receptor (HER2) protein. This biosensor serves as a proof-of-concept of the ability of BN-GO gel FETs to be used for ultrasensitive biosensors.

[Prevalence of Spirometra mansoni infections in hosts in Jiangsu Province].

OBJECTIVE: To investigate the prevalence of Spirometra mansoni infections in hosts in Jiangsu Province, so as to provide the scientific basis for the management of sparganosis mansoni. METHODS: From 2018 to 2019, nine counties (cities, districts) were randomly selected from Jiangsu Province as the survey sites, and 100 healthy individuals were randomly selected to perform the serological test of S. mansoni infections and the detection of S. mansoni eggs. The procercoids were detected in the intermediate host Cyclops, and the S. mansoni eggs were identified in the stool samples of the definitive hosts cats and dogs. RESULTS: The prevalence of S. mansoni human infections was 0 (0/900) in the 9 survey sites of Jiangsu Province, and the sero-prevalence of the specific IgG antibody against S. mansoni was 1.22% (11/900). The positive rate of procercoids was 0.33% (3/900) in Cyclops. In addition, the S. mansoni egg-positive rate was 1.48% (2/135) in cats and dogs. CONCLUSIONS: Sparganosis mansoni is prevalent in Jiangsu Province. Health education pertaining to the damages of sparganosis mansoni and the route of S. mansoni infections should be improved.

Synthesis of MoS2/g-C3N4 nanocomposites with enhanced visible-light photocatalytic activity for the removal of nitric oxide (NO).

Molybdenum disulfide and graphitic carbon nitride (MoS2-g-C3N4) nanocomposites with visible-light induced photocatalytic activity were successfully synthesized by a facile ultrasonic dispersion method. The crystalline structure and morphology of the MoS2-g-C3N4 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microcopy (TEM), high-resolution TEM (HRTEM) and scanning electron microscopy (SEM). The optical property of the as-prepared nanocomposites was studied by ultraviolet visible diffusion reflection (UV-vis) and photoluminescence(PL) spectrum. It could be observed from the TEM image that the MoS2 nanosheets and g-C3N4 nanoparticles were well combined together. Moreover, the photocatalytic activity of MoS2-g-C3N4 composites was evaluated by the removal of nitric oxide under visible light irradiation (>400nm). The experimental results demonstrated that the nanocomposites with the MoS2 content of 1.5 wt% exhibited optimal photocatalytic activity and the corresponding removal rate of NO achieved 51.67%, higher than that of pure g-C3N4 nanoparticles. A possible photocatalytic mechanism for the MoS2-g-C3N4 nanocomposites with enhanced photocatalytic activity could be ascribed to the hetero-structure of MoS2 and g-C3N4.

Clinical analysis of cases of neonatal Streptococcus agalactiae sepsis.

With the advent of antibiotic resistance, pathogenic bacteria have become a major threat in cases of neonatal sepsis; however, guidelines for treatment have not yet been standardized. In this study, 15 cases of neonatal Streptococcus agalactiae sepsis from our hospital were retrospectively analyzed. Of these, nine cases showed early-onset and six cases showed late-onset sepsis. Pathogens were characterized by genotyping and antibiotic sensitivity tests on blood cultures. Results demonstrated that in cases with early-onset sepsis, clinical manifestations affected mainly the respiratory tract, while late-onset sepsis was accompanied by intracranial infection. Therefore, we suggest including a cerebrospinal fluid examination when diagnosing neonatal sepsis. Bacterial genotyping indicated the bacteria were mainly type Ib, Ia, and III S. agalactiae. We recommend treatment with penicillin or ampicillin, since bacteria were resistant to clindamycin and tetracycline. In conclusion, our results provide valuable information for the clinical treatment of S. agalactiae sepsis in neonatal infants.

Friction measurement on free standing plates using atomic force microscopy.

A method is introduced to measure friction on small, free standing objects, specifically microfabricated silicon plates, based on atomic force microscopy (AFM). An AFM tip is brought into contact with the plate resting on a substrate. The substrate is displaced laterally and, provided the AFM tip does not slide over the plate, the twisting of the AFM cantilever is used to measure the friction of the underlying plate-substrate interface. The method can measure nano-Newton to micro-Newton forces (both friction and applied load) and provides a means to measure friction of macroscopic structures at low load.

Electroplated CoPt magnets for actuation of stiff cantilevers.

A cantilever has been microfabricated for use in non-contact Atomic Force Microscopy (AFM) using a very thick magnetic film to actuate the cantilever motion. The thick magnetic block is deposited electrochemically over a defined area of the cantilever. This cantilever is particularly suitable for driving stiff AFM cantilevers in a liquid environment. Clean mechanical resonances are easily observed. Examples are given of a hard (CoPt) magnet of dimension 29 × 21 × 6 µm(3) electroplated on Silicon cantilevers of stiffness ~22 N/m, giving a static displacement of ~0.2 nm in an applied field of 10(-3) T.

Structure of a histidine ligand in the photosynthetic oxygen-evolving complex as studied by light-induced fourier transform infrared difference spectroscopy.

Fourier transform infrared (FTIR) signals of a histidine side chain were identified in flash-induced S(2)/S(1) difference spectra of the oxygen-evolving complex (OEC) of photosystem II (PS II) using PS II membranes from globally (15)N-labeled spinach and PS II core complexes from Synechocystis cells in which both the imidazole nitrogens of histidine were selectively labeled with (15)N. A negative band at 1113-1114 cm(-1) was downshifted by 7 cm(-1) upon both global (15)N-labeling and selective [(15)N]His labeling, and assigned to the C-N stretching mode of the imidazole ring. This band was unaffected by H-D exchange in the PS II preparations. In addition, several peaks observed at 2500-2850 cm(-1) all downshifted upon global and selective (15)N-labeling. These were ascribed to Fermi resonance peaks on a hydrogen-bonding N-H stretching band of the histidine side chain. FTIR measurements of model compounds of the histidine side chain showed that the C-N stretching band around 1100 cm(-)(1) can be a useful IR marker of the protonation form of the imidazole ring. The band appeared with frequencies in the following order: Npi-protonated (>1100 cm(-1)) > imidazolate > imidazolium > Ntau-protonated (<1095 cm(-1)). The frequency shift upon N-deuteration was occurred in the following order: imidazolium (15-20 cm(-1)) > Ntau-protonated (5-10 cm(-1)) > Npi-protonated approximately imidazolate ( approximately 0 cm(-1)). On the basis of these findings together with the Fermi resonance peaks at >2500 cm(-1) as a marker of N-H hydrogen-bonding, we concluded that the histidine residue in the S(2)/S(1) spectrum is protonated at the Npi site and that this Npi-H is hydrogen bonded. This histidine side chain probably ligated the redox-active Mn ion at the Ntau site, and thus, oxidation of the Mn cluster upon S(2) formation perturbed the histidine vibrations, causing this histidine to appear in the S(2)/S(1) difference spectrum.

An electron spin-echo envelope modulation (ESEEM) study of the QA binding pocket of PS II reaction centers from spinach and Synechocystis.

We have used electron spin-echo envelope modulation spectroscopy (ESEEM) to characterize the protein-cofactor interactions present in the QA- binding pocket of PS II centers isolated from spinach and Synechocystis. We conclude that the ESEEM spectrum of QA- is the result of interactions of the S = 1/2 electron spin of QA- with the I = 1 nuclear spins of the peptide nitrogens of two different amino acids. One peptide nitrogen has ESEEM peaks near 0.7, 2.0, 2.85, and 5.0 MHz with isotropic and dipolar hyperfine couplings of Aiso = 2.0 MHz and Adip = 0.25 MHz, respectively. On the basis of these hyperfine couplings we predict the existence of a strong hydrogen bond between QA- and the peptide nitrogen with a hydrogen bond distance of about 2 A. We have not identified the amino acid origin of this peptide nitrogen. By using amino acid specific isotopic labeling in conjunction with site-directed mutagenesis, we demonstrate that the second peptide nitrogen is that of D2-Ala260, with ESEEM peaks near 0.6 and 1.5 MHz and an isotropic hyperfine coupling, Aiso, less than 0.2 MHz. This small isotropic coupling suggests that the D2-Ala260 peptide nitrogen at best forms a weak hydrogen bond with QA-.

Hydrogen bonding interaction between the primary quinone acceptor QA and a histidine side chain in photosystem II as revealed by Fourier transform infrared spectroscopy.

Interactions of the primary quinone acceptor QA of photosystem II (PS II) with surrounding amino acid residues were studied by analysis of FTIR difference spectra of QA upon its photoreduction (QA-/QA). Structural coupling with a His side chain was revealed by identifying the imidazole bands in the QA-/QA spectrum using the PS II core complexes from Synechocystis PCC 6803 in which both of the two imodazole nitrogens of His side chains were specifically labeled with 15N. Strong hydrogen bonding of the imidazole NH was shown by (i) the presence of several peaks at 2600-3000 cm-1, which arise from Fermi resonance of harmonics or combinations of imidazole ring modes with the hydrogen bonding NH stretching vibration, and (ii) the 1179 cm-1 band, which can be assigned to the mode including NH deformation, is at a frequency significantly higher than the corresponding 1151 cm-1 band of model compounds 4- and 5-methylimidazole in aqueous solution. Also, the presence of the bands specific to the Npi-protonated state at 1109/1102/1090 and 1359 cm-1 suggests that the QA-coupled His is protonated at the Npi site. These results are in good agreement with the model of QA interaction in which His215 (D2), which coordinates to the non-heme iron at Ntau, is hydrogen bonded to the QA carbonyl through the Npi-H bond. In contrast, no bands of Trp side chains were detected in the QA-/QA spectrum upon labeling of the indole ring of Trp residues with indole-d5. This result indicates that Trp254 (D2), which corresponds to Trp252 (M) of the bacterial reaction center that is located in van der Waals contact with QA, is not strongly coupled with QA in PS II. Probably, the predicted pi-pi interaction is not strong enough to influence the vibrations of the indole ring of Trp upon QA reduction, or Trp254 (D2) is located rather far from QA in PS II.

Structural coupling between the oxygen-evolving Mn cluster and a tyrosine residue in photosystem II as revealed by Fourier transform infrared spectroscopy.

The flash-induced Fourier transform infrared (FTIR) difference spectrum of the oxygen-evolving Mn cluster upon S1-to-S2 transition (S2/S1 spectrum) was measured using photosystem II (PS II) core complexes of Synechocystis 6803 in which tyrosine residues were specifically labeled with 13C at the ring-4 position. The double-difference spectrum between the unlabeled and labeled S2/S1 spectra showed that the bands at 1254 and 1521 cm-1 downshifted by 25 and 15 cm-1, respectively, upon ring-4-13C-Tyr labeling. This observation indicates that there is a tyrosine residue coupled to the Mn cluster, and the vibrational modes of this tyrosine are affected upon S2 formation. From a comparison of the above band positions and isotopic shifts in the S2/S1 spectrum with those of the FTIR spectra of tyrosine in aqueous solution at pH 0.6 (Tyr-OH) and pH 13.4 (Tyr-O-) and of the YD./YD FTIR difference spectrum, the 1254 and 1521 cm-1 bands were assigned to the CO stretching and ring CC stretching modes of tyrosine, respectively, and this tyrosine was suggested to be protonated in PS II. The observation that the effect of the S2 formation on the tyrosine bands appeared as a decrease in intensity with little frequency change could not be explained by a simple electrostatic effect by Mn oxidation, suggesting that the Mn cluster and a tyrosine are linked via chemical and/or hydrogen bonds and the structural changes of the Mn cluster are transmitted to the tyrosine through these bonds. On the basis of previous EPR studies that showed close proximity of YZ to the Mn cluster, YZ was proposed as the most probable candidate for the above tyrosine. This is the first demonstration of the structural coupling between YZ and the Mn cluster in an intact oxygen-evolving complex. This structural coupling may facilitate electron transfer from the Mn cluster to YZ. Our observation also provides an experimental support in favor of the proton or hydrogen atom abstraction model for the YZ function.

Identification of histidine as an axial ligand to P700+.

The primary electron donor in photosystem I (PSI), P700, is thought to be a dimeric Chl a species. Neither the electronic nor geometric structure of the cation radical is clearly understood. Magnetic resonance studies have indicated that the unpaired electron in P700+ is delocalized asymmetrically over the Chl dimer; however, the axial ligand to the central Mg2+ is not known. The recent development of a histidine tolerant mutant of Synechocystis PCC 6803 has allowed us to use a combination of isotopic labeling and electron nuclear double resonance (ENDOR) spectroscopy to show the first definitive spectroscopic evidence of a histidine ligand to P700+. Peaks split symmetrically about the 15N Larmor frequency corresponding to an isotropic hyperfine coupling of 0.64 MHz were observed in the ENDOR spectra from P700+ globally labeled with 15N and specifically labeled with [15N]histidine. These peaks disappeared in "reverse" labeled samples in which all nitrogens are 15N except those of histidine, which contains natural abundance 14N. The dipolar contribution to the hyperfine coupling was determined by using electron spin echo envelope modulation spectroscopy (ESEEM). Numerical simulations of the ESEEM data suggest that the coupling is primarily isotropic and that the histidine is directly coordinated to the central Mg2+ of P700+. Taken together, these data are supportive of a model of P700+ in which the excited state molecular orbital makes a significant contribution to the electronic structure of the radical. Moreover, the methodology developed in this work can be extended to examine the magnetic properties of axial ligands in a variety of biologically relevant porphyrin/chlorin systems.

Investigation of the differences in the local protein environments surrounding tyrosine radicals YZ. and YD. in photosystem II using wild-type and the D2-Tyr160Phe mutant of Synechocystis 6803.

The reaction center of photosystem II (PSII) of the oxygenic photosynthetic electron transport chain contains two redox-active tyrosines, Tyr160 (YD) of the D2 polypeptide and Tyr161 (YZ) of the D1 polypeptide, each of which may be oxidized by the primary electron donor, P680+. Spectroscopic characterization of YZ. has been hampered by the simultaneous presence of the much more stable YD., the short lifetime of YZ., and the difficulty in trapping the YZ. radical at low temperature. We present here a method for obtaining an uncontaminated YZ. radical, trapped by freezing under illumination of PSII core complexes isolated from YD-less mutants of Synechocystis 6803. Specific labeling with deuterium of the beta-methylene-3,3- or of the ring 3,5-protons of the PSII reaction center tyrosines in the YD-less D2-Tyr160Phe mutant results in a change in the hyperfine structure of the YZ. EPR signal, further confirming that this signal indeed arises from tyrosine. The trapped YZ. radical is also stable for several months at liquid nitrogen temperature. Due to both the absence of contaminating paramagnetic species and the stability at low temperature of YZ., this mutant core complex constitutes an excellent experimental system for the spectroscopic analysis of YZ.. We have compared the environments of YZ. and YD. by EPR, 1H ENDOR, and TRIPLE spectroscopies using both mutant and wild-type core complexes, with the following observations: (1) the EPR spectra of YZ. and YD. differ in line shape and line width. (2) Both YZ. and YD. exhibit D2O-exchangeable 1H hyperfine coupling near 3 MHz, consistent with the presence of a hydrogen bond from a proton donor to the phenolic oxygen atom of a neutral tyrosyl radical. This hyperfine coupling is sharp in the case of YD., indicating the hydrogen bond to be well-defined. In the case of YZ. it is broad, suggestive of a distribution of hydrogen-bonding distances. (3) YD. possesses three additional weak couplings that disappear in D2O, arising from three or fewer protons (protein or solvent) located within a shell between 4.5 and 8.5 A. (4) All of the 1H couplings of YD. are sharp, which is indicative of a well-ordered protein environment. (5) All of the 1H couplings in the YZ. spectrum are broad. The environment surrounding YZ. appears to be more disordered and solvent-accessible.

245 GHz high-field EPR study of tyrosine-D zero and tyrosine-Z zero in mutants of photosystem II.

A 245 GHz 8.7 T high-field EPR study of tyrosine-D (TyrD zero) and tyrosine-Z (TyrZ zero) radicals of photosystem II (PSII) from Synechocystis PCC 6803 was carried out. Identical principal g values for the wild-type Synechocystis and spinach TyrD zero showed that the two radicals were in similar electrostatic environments. By contrast, the principal g values of the TyrD zero in the D2-His189Gln mutant of Synechocystis were different from those of the wild-type and spinach radicals and were similar to those of the tyrosyl radical in ribonucleotide reductase. These comparisons indicate that the D2-His189Gln mutant TyrD zero is not hydrogen-bonded or is only weakly so. The HF-EPR spectrum of TyrZ zero was obtained from the D2-Tyr160Phe mutant that lacks TyrD zero. The principal g values were nearly identical to those of the wild-type TyrD zero. The low-field edge of the TyrZ zero spectrum was much broader than at the other two principal g values and was also much broader than the TyrD zero spectrum. From the identical g values and previous work on tyrosyl radical g values [Un S., Atta M., Fontecave, M., & Rutherford, A. W. (1995) J. Am. Chem. Soc. 117, 10713-10719], it was concluded that TyrZ zero, like TyrD zero, is hydrogen-bonded The broadness of the gx component was interpreted as a distribution in strength of the hydrogen-bonding due to disorder in the protein environment about TyrZ zero.

Spectroscopic evidence for the symmetric location of tyrosines D and Z in photosystem II.

Saturation-recovery EPR spectroscopy has been used to probe the location of the redox-active tyrosines, YD (tyrosine 160 of the D2 polypeptide, cyanobacterial numbering) and YZ (tyrosine 161 of the D1 polypeptide), relative to the non-heme Fe(II) in Mn-depleted photosystem II (PSII). Measurements have been made on PSII membranes isolated from spinach and on PSII core complexes purified from the cyanobacterium Synechocystis sp. PCC 6803. In the case of Synechocystis PSII, site-directed mutagenesis of the YD residue to either phenylalanine (Y160F) or methionine (Y160M) was done to eliminate the dark-stable YD.species and, thereby, allow direct spectroscopic observation of the YZ. EPR signal. The spin-lattice relaxation transients of both YD. and YZ. were non-single-exponential due to a dipolar interaction with one of the other paramagnetic species in PSII. Measurements on CN(-)-treated, Mn-depleted cyanobacterial PSII, in which the non-heme Fe(II) was converted into its low-spin, diamagnetic state, proved that the non-heme Fe(II) was the sole spin-lattice relaxation enhancer for both the YD. and YZ. radicals. This justified the use of a dipolar model in order to fit the saturation-recovery EPR data, which were taken over the temperature range 4-70 K. The dipolar rate constants extracted from the fits were identical in magnitude and had the same temperature dependence for both YD. and YZ.. The observation of identical dipolar interactions between YD. and YZ. and the non-heme Fe(II) shows that the distance from each tyrosine to the non-heme Fe(II) is the same.(ABSTRACT TRUNCATED AT 250 WORDS)

A hydrogen-atom abstraction model for the function of YZ in photosynthetic oxygen evolution.

Recent magnetic-resonance work on YZ suggests that this species exhibits considerable motional flexibility in its functional site and that its phenol oxygen is not involved in a well-ordered hydrogen-bond interaction (Tang et al., submitted; Tommos et al., in press). Both of these observations are inconsistent with a simple electron-transfer function for this radical in photosynthetic water oxidation. By considering the roles of catalytically active amino acid radicals in other enzymes and recent data on the water-oxidation process in Photosystem II, we rationalize these observations by suggesting that YZ functions to abstract hydrogen atoms from aquo- and hydroxy-bound managanese ions in the (Mn)4 cluster on each S-state transition. The hydrogen-atom abstraction process may occur either by sequential or concerted kinetic pathways. Within this model, the (Mn)4/YZ center forms a single catalytic center that comprises the Oxygen Evolving Complex in Photosystem II.

Biochemical and spectroscopic characterization of a new oxygen-evolving photosystem II core complex from the cyanobacterium Synechocystis PCC 6803.

We describe here a new procedure permitting rapid (12-13 h) isolation of a pure oxygen-evolving photosystem II (PSII) core complex from the cyanobacterium Synechocystis PCC 6803. This procedure involves dodecyl maltoside extraction of thylakoid membranes followed by single-step column chromatography using a weak anion-exchanger. SDS-PAGE and immunoblotting show that the complex consists of five intrinsic membrane proteins (CP47, CP43, D1, D1, and cyt b559), one extrinsic protein (MSP), and one unknown protein with a molecular mass of approximately 26 kDa. A chemical and functional analysis, normalized to 2 molecules of pheophytin a, indicates that this PSII core complex contains 1 photoactive plastoquinone, QA, 4 manganese atoms, 38 chlorophyll a molecules, 1 cytochrome b559, 2 plastoquinone-9, and 9-10 beta-carotenes. The complex exhibits high rates of oxygen evolution, typically 2400-2600 mumol of O2 (mg of Chl)-1 h-1 in the presence of 2,5-dichlorobenzoquinone as an artificial electron acceptor with a pH optimum of 6.5. A strong light minus dark multiline EPR signal, arising from the S2 state of the oxygen-evolving complex (OEC), is observed at 10 K following illumination at 198 K. The determination of the absolute oxygen yield per saturating microsecond flash indicates that essentially all of the PSII centers contain functional oxygen-evolving complexes. This point is further supported by the absence of photoaccumulation, upon room temperature illumination, of the immediate oxidant of the OEC, redox-active tyrosine, YZ.. On the basis of EPR spectra, oxidized minus reduced difference spectra, and SDS-PAGE, the preparation contains on a per mole basis with PSII only trace amounts of PSI (approximately 0.04), cytochrome b6/f complex (< or = 0.01), and ATPase (< or = 0.05). All of these results indicate that this PSII preparation is to date the most highly purified oxygen-evolving core complex from Synechocystis 6803 that retains all of the reaction centers active for oxygen evolution. As Synechocystis 6803 is being used extensively for site-directed mutagenesis of PSII, this preparation is particularly valuable for spectroscopic and biochemical analyses of PSII from wild-type and from site-directed mutants.