Evaluation of the antidiabetic potential of selected medicinal plant extracts from the Canadian boreal forest used to treat symptoms of diabetes: part II

Among the Cree of northern Quebec, the disproportionately high rate of diabetic complications is largely due to the cultural inadequacy of modern therapies for type 2 diabetes. To establish culturally adapted antidiabetic treatments, our team identified several candidate plant species used by the Cree to treat symptoms of diabetes. An initial study focused on 8 species and revealed that most possess significant in vitro antidiabetic activity. The purpose of the present study was to assess a further 9 species identified through the ethnobotanical survey. Crude plant extracts were screened for (i) potentiation of basal and insulin-stimulated glucose uptake by skeletal muscle cells (C2C12) and adipocytes (3T3-L1); (ii) potentiation of glucose-stimulated insulin secretion by pancreatic β cells (βTC); (iii) potentiation of adipogenesis in 3T3-L1 cells; (iv) protection against glucose toxicity and glucose deprivation in PC12-AC neuronal precursor cells; and (v) diphenylpicrylhydrazyl (DPPH) oxygen free radical scavenging. Four species potentiated basal glucose uptake in muscle cells or adipocytes, one species being as potent as metformin. Adipogenesis was accelerated by 4 species with a potency roughly half that of rosiglitazone. Five species protected PC12-AC cells against glucose toxicity and 4 protected against glucose deprivation. Five species exhibited antioxidant activity comparable to ascorbic acid. However, no species increased insulin secretion. The present study revealed that Gaultheria hispidula , Rhododendron tomentosum , and Vaccinium vitis-idaea exhibit a promising profile of antidiabetic potential and are good candidates for more in-depth evaluation.

Microdosing imaging pharmacokinetic (PK) study of the antisense oligonucleotide (ASO) to survivin (LY2181308) using positron emission tomography (PET): A novel paradigm in clinical drug development

3578

Background: Survivin, an inhibitor of an apoptosis protein, widely overexpressed in cancer is associated with poor clinical outcome. We performed the first worldwide human microdosing imaging PK study of an ASO with LY2181308, a specific, second generation antisense inhibitor of Survivin using carbon-11 radiolabelled LY2181308 ([11C]LY2181308). Methods: LY2181308 was administered at the recommended phase II dose (750 mg over 3 hours IV daily x 3, then once weekly). [11C]LY2181308 was manufactured to GMP standard by random [11C]methylation with [11C]methyl iodide of LY2181308 using a GE Tracerlab FXc molecule. [11C]LY2181308-PET scans were performed at baseline and during treatment infusion. [11C]LY2181308 uptake in normal tissue and tumour was quantified. Results: Three pts (2 female Caucasian/1 male Asian) were scanned after administering [11C]LY2181308 which delivered (135–376 μg) of LY2181308. Despite its large size (6778 amu), [11C]LY2181308 rapidly distributed to tissues, with maximal uptake in kidney followed by liver, spleen, vertebral body, tumour, spinal cord, lung, and muscle at baseline. Although renal uptake was high, urinary elimination (bladder activity) was low suggesting renal trapping of [11C]LY2181308 at baseline. For a normalised injected dose of 1 mg, mean (range) tumour concentrations of 31 (4–41) ng/ml were observed at baseline, consistent with that predicted from the preclinical PK/PD model. In a pt with mesothelioma who also had a second [11C]LY2181308-PET scan during LY2181308 treatment infusion, there was about 2-fold increase in [11C]LY2181308 tumour uptake, in contrast to markedly reduced uptake in kidneys, liver, and spleen and similar aortic (circulatory) [11C]LY2181308 levels. In this patient, tumour [18F]FDG- PET uptake at 28 days was reduced by up to 40% after treatment, suggesting drug activity. Conclusions: [11C]LY2181308 pharmacokinetics suggest biologically active human tumour drug concentrations can be attained. LY2181308 therapy saturated normal tissue kinetics and increased tumour uptake of [11C]LY2181308. Data uniquely obtained from fully regulated microdosing studies may rationalise and hasten drug development.

[Table: see text]

A PET imaging study of the vascular disruptive agent OXi4503 to confirm in vivo mechanism of action in a phase I trial

e14510

Background: OXi4500, the active product of OXi4503, reversibly binds at the colchicine binding site on the ß subunit of tubulin. This study investigated its mechanism of action using PET molecular imaging Methods: OXi4503 was administered by 3 weekly IV infusions in a phase 1 trial (32 pts). Between 1.6 & 15.4 mg/m2 dose levels, PET imaging was performed with 15O-labelled water (measuring blood perfusion) pretreatment & at 90min & 24hr after first infusion (8pts) & at 28days (1 pt). [18F]fluorodeoxyglucose (FDG) (measuring proliferative activity) was performed pretreatment & at 28 days (9pts) Results: 9 pts (mean age 48.5yrs) were studied: CRC (2), pancreatic (1), MM (6). 2 pts with MM (3.8 & 6.5 mg/m2) achieved stable disease. Toxicity included pyrexia, lethargy & hypertension. There was a dose-dependent linear increase in peak plasma concentrations & AUC of OXi4503 & OXi4500. Sustained tumour blood perfusion reduction (50% at 90min & 24hr) was seen in all metastases in the CRC pt treated at 15.4 mg/m2 after just one dose & resulted in FDG reduction (23% in all 5 mets) & tumor marker response. Doses between 1.9 & 11.0 mg/m2 produced dose independent reductions in tumour perfusion which were more variable & less marked with 3/8 pts showing a reduction in tumour FDG uptake. The 1pt studied at 28 days (8.5 g/m2) showed further sustained reduction in tumour blood flow (40%). Variable dose independent changes in normal tissue perfusion were seen at all dose levels eg in 3/4 pt splenic perfusion showed a dose-independent decrease (20–30%) at 90min with recovery at 24hr Conclusions: OXi4503 shows significant activity at 15.4 mg/m2 in line with its proposed mechanism of action. Characterisation of the mixed tumour perfusion response at lower doses will aid planning & assessing combination studies. The MTD is now being identified. Sponsored by CRUK.

[Table: see text]

Root colonization by an arbuscular mycorrhizal (AM) fungus increases growth and secondary metabolism of purple coneflower, Echinacea purpurea (L.) Moench

Purple coneflower, Echinacea purpurea (L.) Moench, is an important phytomedicinal species that contains phenolics and alkamides with antipathogenic properties. This study aimed to examine the effect of arbuscular mycorrhizal (AM) colonization on the physiology and biochemistry of E. purpurea. It was hypothesized that AM colonization enhances the growth and secondary metabolism in E. purpurea. In this regard, a 13-week factorial greenhouse experiment was performed with E. purpurea, inoculated (or not) with the AM fungus Glomus intraradices Schenck & Smith. Overall, the results indicated that AM colonization significantly increased the mass of shoots and roots and the concentrations of proteins and most of the phenolics in the roots. Hence, the selected trait of mycorrhiza could play an important role in optimizing the growth of E. purpurea by inducing the production of secondary phytomedicinal metabolites.

Seasonal phytochemical variation of anti-glycation principles in lowbush blueberry (Vaccinium angustifolium)

Diabetic hyperglycaemia promotes the production of advanced glycation end-products (AGEs), which play a significant role in the development of complications associated with type 2 diabetes mellitus. Vaccinium angustifolium, a medicinal plant used for the treatment of diabetes, produces a variety of phenolic metabolites with putative anti-diabetic activities. To assess optimal cultivation time, seasonal changes in the concentration of six phenolic compounds in leaves and twelve compounds in stems were examined using HPLC-DAD and examined in relation to seasonal changes in AGE inhibition activity, assessed with a fluorescence-based assay. A seasonal decline occurred in the concentration of chlorogenic acid, rutin, and quercetin 3-arabinoside in leaves and chlorogenic acid in stems. The concentration of (+)-catechin, and (-)-epicatechin in stems declined within two weeks before rising and fluctuating insignificantly. AGE inhibition activity of leaves was significantly greater at the final compared to the initial collection date whereas the activity of stems did not change significantly. Relative to the leaf extract, the stem was a more potent inhibitor of AGE formation, which could be a result of the unique phytochemistry of stems. Together, these results revealed significant seasonal variation in the phenolic profile and anti-glycation effects of V. angustifolium extracts and indicated late summer as the collection time yielding optimal activity.

EMAAS: an extensible grid-based rich internet application for microarray data analysis and management

Background

Microarray experimentation requires the application of complex analysis methods as well as the use of non-trivial computer technologies to manage the resultant large data sets. This, together with the proliferation of tools and techniques for microarray data analysis, makes it very challenging for a laboratory scientist to keep up-to-date with the latest developments in this field. Our aim was to develop a distributed e-support system for microarray data analysis and management.

Results

EMAAS (Extensible MicroArray Analysis System) is a multi-user rich internet application (RIA) providing simple, robust access to up-to-date resources for microarray data storage and analysis, combined with integrated tools to optimise real time user support and training. The system leverages the power of distributed computing to perform microarray analyses, and provides seamless access to resources located at various remote facilities. The EMAAS framework allows users to import microarray data from several sources to an underlying database, to pre-process, quality assess and analyse the data, to perform functional analyses, and to track data analysis steps, all through a single easy to use web portal. This interface offers distance support to users both in the form of video tutorials and via live screen feeds using the web conferencing tool EVO. A number of analysis packages, including R-Bioconductor and Affymetrix Power Tools have been integrated on the server side and are available programmatically through the Postgres-PLR library or on grid compute clusters. Integrated distributed resources include the functional annotation tool DAVID, GeneCards and the microarray data repositories GEO, CELSIUS and MiMiR. EMAAS currently supports analysis of Affymetrix 3' and Exon expression arrays, and the system is extensible to cater for other microarray and transcriptomic platforms.

Conclusion

EMAAS enables users to track and perform microarray data management and analysis tasks through a single easy-to-use web application. The system architecture is flexible and scalable to allow new array types, analysis algorithms and tools to be added with relative ease and to cope with large increases in data volume.

Characterization and Quantification of Triterpenes in the Neotropical Medicinal Plant Souroubea sympetala (Marcgraviaceae) by HPLC-APCI-MS

A rapid, two-solvent, HPLC-APCI-MS method was developed to identify and quantify four pentacyclic triterpenes (betulinic acid, ursolic acid, α-amyrin and β-amyrin) in extracts of the neotropical medicinal plant Souroubea sympetala. Analysis of plant organs, wood, bark, leaves, immature fruit and flowers, indicated that the phytochemical distribution and quantity of triterpenes varies across the plant, with betulinic acid and ursolic acid the major constituents in the bark, wood, fruit and flowers and the amyrins the major constituents of the leaves.

Suboptimal use of intravenous contrast during radiotherapy planning in the UK

We aimed to evaluate the use of intravenous (IV) contrast during acquisition of radiotherapy planning (RTP) scans and to compare current usage with the Royal College of Radiologists' (RCR) recommendations. Questionnaires were circulated via the Academic Clinical Oncology and Radiobiology Research Network (ACORRN) website, email and post to 60 UK radiotherapy centre managers. Questions were asked regarding the (i) tumour sites where IV contrast was used, (ii) person administering the contrast, (iii) availability of dynamic pump, (iv) tumour sites that centres wished to use contrast, (v) reasons for not using contrast and (vi) awareness of RCR recommendations. 50 (83%) centres responded to the questionnaire, of which 27 responded via the ACCORN website and 18 by e-mail. Despite 38 out of 50 responding centres using IV contrast, and accessibility to dynamic pumps existing in 39 centres, IV contrast usage was suboptimal, with more than half of the centres (27/50; 54%) wishing to use it at more tumour sites. IV contrast was most often used during RTP of the brain, with suboptimal usage in lung tumours. None of the 50 centres administered IV contrast during RTP scan acquisition in all of the 8 RCR recommended tumour sites. Radiographers were mainly responsible for contrast administration, and a lack of staff was cited as the main reason for suboptimal contrast usage. Disappointingly, only 35 of the 50 radiotherapy managers (70%) were aware of the RCR recommendations. Redress of the underlying reasons for suboptimal IV contrast administration during RTP, including acquisition of the necessary skill mix by staff and implementation of RCR recommendations, would help standardize UK practice.

Phytochemical Analysis of Nunavik Rhodiola rosea L

This is the first report on the phytochemistry of Nunavik (Québec, Canada) populations of Rhodiola rosea L., a medicinal plant widely used in Eurasia as a tonic and adaptogen. The wild harvested rhizome of the Nunavik populations contained the marker phytochemicals (salidroside, rosarin, rosavin and rosin) reported in authentic Eurasian material, although in lesser amount. Phytochemical profiling by HPLC of the Nunavik populations also showed the presence of new marker compounds not found in the Eurasian material. For quantitative analysis of the phytochemicals, method validation was undertaken, and the marker phytochemicals were measured in the rhizome, leaf, stem, and seeds. The rhizome showed the highest amount of salidroside and rosavins, as well as the highest total phytochemical content. Consequently, the rhizome remains the most medicinally valuable part of R. rosea.

Ecological and physiological studies on soil fungi at Western region, libya

Sixty three species and 5 varieties belonging to 30 fungal genera were collected from 75 soil samples. Cultivated (29 genera and 58 species + 5 var.), desert (22 and 35 + 2 var.) and saline soil (21 and 41 + 1 var.) fungi were recovered on glucose-, cellulose- and 50% sucrose-Czapek's agar at 28℃. The most common genera were Alternaria, Aspergillus, Emericella, Fusarium, Mycosphaerella, Nectria and Penicillium. The most prevalent species from the three types of soils on the three types of media were Alternaria alternata, Aspergillus flavus, A. fumigatus, A. niger, A. terreus, Emericella nidulans, Fusarium oxysporum, Mycosphaerella tassiana, Nectria haematococca and Penicillium chrysogenum. Chaetomium globosum was in the top of fungi in producing endo-β-1,4-glucanases among the 42 tested isolates obtained from soils on cellulose-Czapek's agar. Maximum production of this enzyme by C. globosum obtained after 6 days of incubation at 30℃ with culture medium containing maltose as a carbon source and ammonium nitrate as a nitrogen source and pH initially adjusted to 6.

Plasma pharmacokinetic evaluation of cytotoxic agents radiolabelled with positron emitting radioisotopes

PURPOSE

This study aimed to evaluate the utility of plasma pharmacokinetic analyses of anti-cancer agents from data obtained during positron emission tomography (PET) oncology studies of radiolabelled anti-cancer agents.

PATIENTS AND METHODS

Thirteen patients were administered fluorine-18 radiolabelled 5-FU ([(18)F]5-FU) admixed with 5-FU, corresponding to a total 5-FU dose of 380-407 mg/m2 (eight patients) and 1 mg/m2 (five patients). Nine patients received 2.2-19.2 microg/m2 of carbon-11 radiolabelled N-[2-(dimethylamino)ethyl]acridine-4-carboxamide ([11C]DACA) at 1/1,000th of phase I dose, as part of phase 0 microdosing study. Radioactivity of parent drug obtained from arterial blood samples, the injected activity of the radiolabelled drug, and the total dose of injected drug were used to obtain plasma drug concentrations. Plasma pharmacokinetic parameters were estimated using model-dependent and model-independent methods.

RESULTS

5-FU plasma concentrations at therapeutic doses were above the Km and a single compartment kinetic model was best used to fit the kinetics, with a mean half-life of 8.6 min. Clearance and volumes of distribution (Vd) obtained using both model-dependent and model-independent methods were similar. Mean (SE) clearance was 1,421(144), ml min(-1) and 1,319 (119) ml min(-1) and the mean (SE) Vd was 17.3 (1.8) l and 16.3 (1.9) l by the model-independent method and model-dependent methods, respectively. In contrast, with 1 mg/m2, plasma concentrations of 5-FU were less than the Km and a two-compartment model was used to best fit the kinetics, with the mean 5-FU half-life of 6.5 min. The mean (SE) clearances obtained by the model-independent method and model-dependent methods were 3,089 (314) ml min(-1) and 2,225 (200) ml min(-1), respectively and the mean (SE) Vd were 27.9 (7.0) l and 2.3 (0.4) l, by the model independent and dependent methods, respectively. Extrapolation of AUC0-Clast to AUC0-infinity was less than 3% in both these cohort of patients. A two-compartment model with a mean half-life of 42.1 min was used to best fit the kinetics of DACA; considerable extrapolation (mean 26%) was required to obtain AUC0-infinity from AUC0-Clast. Mean (SE) clearance of DACA was 1,920 (269) ml min(-1), with the model-independent method and 1,627 (287) ml min(-1) with the model-dependent method. Similarly, Vd [mean (SE)] of DACA with the model-independent and model-dependent methods were 118 (22) l and 50 (15) l, respectively.

CONCLUSIONS

Pharmacokinetic parameters can be estimated with confidence from PET studies for agents given at therapeutic doses, whose half-lives are significantly less than the total sampling time during the scan. Tracer studies performed alone, wherein plasma levels below the Km are expected, may also provide valuable information on drug clearance for the entire range of linear kinetics. However, drugs with half-lives longer than the sampling duration are inappropriate for PET plasma pharmacokinetic evaluation.

Phase I evaluation of OXi4503, a vascular disrupting agent, in patients with advanced solid tumours

14146

Background: OXi4500, the active product of OXi4503, is a vascular disrupting agent acting at the colchicine binding site on the β subunit of tubulin. OXi4503 has greater anti-tumour activity in human cancer cell lines, causes a greater reduction in tumour blood flow than combretastatin A4P and has single agent activity in human tumour xenograft models. A phase I trial has commenced to examine the safety, tolerability and pharmacokinetics of OXi4503, with the primary objective being determination of MTD. FDG-PET scans were performed prior to and 28 days after the first infusion of OXi4503. Several other pharmacodynamic endpoints are also being assessed including DCE & BOLD MRI, circulating endothelial progenitor cells and cytokeratin 18. Methods: OXi4503 is administered by 3 weekly iv infusions to a maximum of 6 cycles. Starting dose was 0.06mg/m2. 100% dose escalation in single patient cohorts proceeded to 3.84mg/m2, when cohorts were expanded to three patients and 30% escalation due to emergence of grade 2 drug-related toxicity (thrombocytopaenia). Results: 11 patients have so far received OXi4503 (5F 6M, median age 54, range 33–68); median cycles received was 2 (range 1–4). Common AE’s include hypertension, pyrexia and anaemia. PK profiles show a dose-dependent linear increase in peak plasma concentrations and AUC of both OXi4503 and OXi4500. OXi4500 concentrations at current dosing (5 mg/m2) are close to that seen at the MTD in rats and dogs. DCE-MRI showed significant reduction in Ktrans in one patient (0.24mg/m2). In the 2 patients studied to date, PET images showed a decrease in the standardised uptake value (SUV) in 3 out of 4 metastases for one subject (1.92mg/m2) and in 5 out of 7 metastases for the other subject (3.84mg/m2) demonstrating a reduction in FDG uptake following drug treatment. Of 10 patients assessed, 2 have stable disease and 8 disease progression. Conclusions: OXi4503 has been tolerated at doses up to 5mg/m2 with no DLT observed, but changes in functional activity have been seen in 3 patients. MTD has not been reached and recruitment is ongoing.

[Table: see text]

Epilepsy: public knowledge and attitude in a slum area of Karachi, Pakistan

BACKGROUND

Epilepsy is a common but widely misunderstood illness. Consequently, epileptics suffer from considerable stigmatization in society. Since no studies have detailed the misperceptions about epilepsy in our community, it is not possible to provide focused intervention aimed at eliminating this prejudice.

PURPOSE

To assess the knowledge and attitude regarding epilepsy in an adult population of a Karachi slum area.

METHODS

A face-to-face interview was conducted on 487 consenting adult non-epileptics (305 males; 182 females) who were conveniently sampled. Chi-square test was employed to calculate the variability in knowledge and attitude with demographic and other variables.

RESULTS

In all, 12.5% had never heard about epilepsy. Among the rest, 66.7% identified epilepsy as being non-infectious, while 28.2% were unaware of any treatment available for it. Among the other 71.8%, 62.7% were aware of the existence of anti-epileptic drugs. Religious/spiritual treatment was chosen as the most effective treatment by 33.1%. Males were more likely to identify epilepsy as being non-infectious (p=0.02). Nearly 18% of the respondents would not object to their child marrying an epileptic, 69.5% did not want to socially isolate the epileptics, 83.1% said epileptics could receive academic education, 85.6% said they could perform activities of daily life and 62.4% said they could become useful members of the society. Those who considered epilepsy to be infectious were more likely to carry negative attitudes towards epilepsy (p<0.01 with four attitudes).

CONCLUSIONS

Considerable gaps exist in the community's knowledge about epilepsy. Some of these may explain the prevalence of negative attitudes towards this ailment.

A single HPLC-PAD-APCI/MS method for the quantitative comparison of phenolic compounds found in leaf, stem, root and fruit extracts of Vaccinium angustifolium

A method was developed for the analysis of Vaccinium angustifolium Ait. (Lowbush blueberry), which is a widely used natural health product, particularly for the treatment of diabetic symptoms. While the anthocyanin content of the fruit has been well characterized, the chemistry of the vegetative parts used in supportive therapy for diabetes has been largely ignored. Using a metabolomics-based approach for compound identification with an emphasis on phenolic metabolites, a single HPLC-PAD-APCI/ MS method was developed for the separation and quantitation of the major metabolites found in the 95% ethanol extracts of leaf, stem, root and fruit. The leaf extract contained high concentrations of chlorogenic acid (approximately 100 microg/mg extract) and a variety of quercetin glycosides that were also detected in the fruit and stem extracts. Flavan-3-ol monomers (+)-catechin and (-)-epicatechin were found in all plant parts but their procyanidin dimers were exclusively identified in the stem and root. The accuracy and precision of the presented method were corroborated by low intra- and inter-day variations in quantitative results in all plant part extracts. Further validation of the extraction and analytical protocols focused on identified compounds with reputed anti-diabetic activity, revealing recoveries greater than 80% and detection limits of 0.12-2.73 microg/mL.

Effect of herbizid and touchdown herbicides on soil fungi and on production of some extracellular enzymes

Glucophilic and cellulose-decomposing fungi were significantly reduced in soil samples treated with 0.019-0.152 mg a.i./kg soil of the herbicides Herbizid and Touchdown. The decrease was regularly correlated with the doses of the two herbicides and persisted till the end of the experiment (12 weeks). The isolated fungi were found to be able to produce hydrolytic extracellular enzymes in solid media but with variable capabilities. The ability to produce enzymes was adversily affected by the incorporation of herbicides in culture media. Lower doses of herbicides were occasionally promotive to enzyme production and mycelial growth of some fungi. Incorporation of 50 ppm of Herbizid and Touchdown significantly activated amylase production and mycelial dry weight in cultures of Fusarium oxysporum, Mucor hiemalis and Penicillium chrysogenum. There was a significant increase in C1-cellulase produced by F. oxysporum and P. aurantiogriseum when cultures were treated with 50, 100 and 200 ppm of Herbizid which induced also more Cx-cellulase production by P. chrysogenum. Lipase and protease production was always lower in treated than in control fungal cultures.

Synthesis and assembly of thylakoid protein complexes: multiple assembly steps of photosystem II

To study the synthesis and assembly of multisubunit thylakoid protein complexes, we performed [35S]Met pulse and chase experiments with isolated chloroplasts and intact leaves of spinach (Spinacia oleracea L.), followed by Blue Native gel separation of the (sub)complexes and subsequent identification of the newly synthesized and assembled protein subunits. PSII (photosystem II) core subunits were the most intensively synthesized proteins, particularly in vitro and at high light intensities in vivo, and could be sequestered in several distinct PSII subassemblies. Newly synthesized D1 was first found in the reaction centre complex that also contained labelled D2 and two labelled low-molecular-mass proteins. The next biggest PSII subassembly contained CP47 also. Then PsbH was assembled together with at least two other labelled chloroplast-encoded low-molecular-mass subunits, PsbM and PsbTc, and a nuclear-encoded PsbR. Subsequently, CP43 was inserted into the PSII complex concomitantly with PsbK. These assembly steps seemed to be essential for the dimerization of PSII core monomers. Intact PSII core monomer was the smallest subcomplex harbouring the newly synthesized 33 kDa oxygen-evolving complex protein PsbO. Nuclear-encoded PsbW was synthesized only at low light intensities concomitantly with Lhcb polypeptides and was distinctively present in PSII-LHCII (where LHC stands for light-harvesting complex) supercomplexes. The PsbH protein, on the contrary, was vigorously synthesized and incorporated into PSII core monomers together with the D1 protein, suggesting an intrinsic role for PsbH in the photoinhibition-repair cycle of PSII.

Dynamics of photosystem II: a proteomic approach to thylakoid protein complexes

Oxygenic photosynthesis produces various radicals and active oxygen species with harmful effects on photosystem II (PSII). Such photodamage occurs at all light intensities. Damaged PSII centres, however, do not usually accumulate in the thylakoid membrane due to a rapid and efficient repair mechanism. The excellent design of PSII gives protection to most of the protein components and the damage is most often targeted only to the reaction centre D1 protein. Repair of PSII via turnover of the damaged protein subunits is a complex process involving (i) highly regulated reversible phosphorylation of several PSII core subunits, (ii) monomerization and migration of the PSII core from the grana to the stroma lamellae, (iii) partial disassembly of the PSII core monomer, (iv) highly specific proteolysis of the damaged proteins, and finally (v) a multi-step replacement of the damaged proteins with de novo synthesized copies followed by (vi) the reassembly, dimerization, and photoactivation of the PSII complexes. These processes will shortly be reviewed paying particular attention to the damage, turnover, and assembly of the PSII complex in grana and stroma thylakoids during the photoinhibition-repair cycle of PSII. Moreover, a two-dimensional Blue-native gel map of thylakoid membrane protein complexes, and their modification in the grana and stroma lamellae during a high-light treatment, is presented.

Dynamics of photosystem II: a proteomic approach to thylakoid protein complexes

Oxygenic photosynthesis produces various radicals and active oxygen species with harmful effects on photosystem II (PSII). Such photodamage occurs at all light intensities. Damaged PSII centres, however, do not usually accumulate in the thylakoid membrane due to a rapid and efficient repair mechanism. The excellent design of PSII gives protection to most of the protein components and the damage is most often targeted only to the reaction centre D1 protein. Repair of PSII via turnover of the damaged protein subunits is a complex process involving (i) highly regulated reversible phosphorylation of several PSII core subunits, (ii) monomerization and migration of the PSII core from the grana to the stroma lamellae, (iii) partial disassembly of the PSII core monomer, (iv) highly specific proteolysis of the damaged proteins, and finally (v) a multi-step replacement of the damaged proteins with de novo synthesized copies followed by (vi) the reassembly, dimerization, and photoactivation of the PSII complexes. These processes will shortly be reviewed paying particular attention to the damage, turnover, and assembly of the PSII complex in grana and stroma thylakoids during the photoinhibition-repair cycle of PSII. Moreover, a two-dimensional Blue-native gel map of thylakoid membrane protein complexes, and their modification in the grana and stroma lamellae during a high-light treatment, is presented.