Purification and spectroscopic characterization of photosystem II reaction center complexes isolated with or without Triton X-100.

The pigment composition of the isolated photosystem II reaction center complex in its most stable and pure form currently is a matter of considerable debate. In this contribution, we present a new method based on a combination of gel filtration chromatography and diode array detection to analyze the composition of photosystem II reaction center preparations. We show that the method is very sensitive for the detection of contaminants such as the core antenna protein CP47, pigment-free and denatured reaction center proteins, and unbound chlorophyll and pheophytin molecules. We also present a method by which the photosystem II reaction center complex is highly purified without using Triton X-100, and we show that in this preparation the contamination with CP47 is less than 0.1%. The results strongly indicate that the photosystem II reaction center complex in its most stable and pure form binds six chlorophyll a, two pheophytin a, and two β-carotene molecules and that the main effect of Triton X-100 is the extraction of β-carotene from the complex. Analysis of 4 K absorption and emission spectra indicates that the spectroscopic properties of this preparation are similar to those obtained by a short Triton X-100 treatment. In contrast, preparations obtained by long Triton X-100 treatment show decreased absorption of the shoulder at 684 nm in the 4 K absorption spectrum and an increased number of pigments that trap excitation energy at very low temperatures. We conclude that the 684 nm shoulder in the 4 K absorption spectrum should at least in part be attributed to the primary electron donor of photosystem II

Supramolecular organization of photosystem II and its light-harvesting antenna in partially solubilized photosystem II membranes

We present an extended analysis of the organization of green plant photosystem II and its associated light-harvesting antenna using electron microscopy and image analysis. The analysis is based on a large dataset of 16 600 projections of negatively stained PSII-LHCII supercomplexes and megacomplexes prepared by means of three different pretreatments. In addition to our previous work on this system [Boekema, E.J., van Roon, H., Calkoen, F., Bassi, R. and Dekker, J.P. (1999) Biochemistry 38, 2233-2239], the following results were obtained. The rotational orientation of trimeric LHCII at the S, M and L binding positions was determined. It was found that compared to the S trimer, the M and L trimers are rotationally shifted by about -20 degrees and -50 degrees, respectively. The number of projections with empty CP29, CP26 and CP24 binding sites was found to be about 0, 18 and 4%, respectively. We suggest that CP26 and CP24 are not required for the binding of trimeric LHCII at any of the three binding positions. A new type of megacomplex was observed with a characteristic windmill-like shape. This type III megacomplex consists of two C2S2 supercomplexes connected at their CP26 tips. Structural variation in the region of the central dimeric photosystem II complex was found to occur at one specific position near the periphery of the complex. We attribute this variation to the partial absence of an extrinsic polypeptide or one or more small intrinsic membrane proteins

JUMPING MODE ATOMIC FORCE MICROSCOPY ON GRANA MEMBRANES FROM SPINACH

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Heptameric association of light-harvesting complex II trimers in partially solubilized photosystem II membranes

We report a structural characterization by electron microscopy and image analysis of a supramolecular complex consisting of seven trimeric light-harvesting complex II proteins, The complex was readily observed in partially-solubilized Tris-washed photosystem II membranes from spinach but was also found to occur, with a low frequency, in oxygen-evolving photosystem II membranes. The structure reveals sis peripheral trimers with the same rotational orientation and a central trimer with the opposite orientation. We conclude that the heptamer represents a naturally occurring aggregation state of part of the light-harvesting complex II trimers in the thylakoid membranes. (C) 1999 Federation of European Biochemical Societies.</p

Predicting recurrence of depression using cardiac complexity in individuals tapering antidepressants

It is currently unknown whether the complexity and variability of cardiac dynamics predicts future depression and whether within-subject change herein precedes the recurrence of depression. We tested this in an innovative repeated single-subject study in individuals who had a history of depression and were tapering their antidepressants. In 50 individuals, electrocardiogram (ECG) derived Interbeat-interval (IBI) time-series data were collected for 5 min every morning and evening, for 4 months. Usable data were obtained from 14 participants who experienced a transition (i.e., a clinically significant increase in depressive symptoms) and 14 who did not. The mean, standard deviation, Higuchi dimension and multiscale entropy, calculated from IBIs, were examined for time trends. These quantifiers were also averaged over a baseline period and compared between the groups. No consistent trends were observed in any quantifier before increases in depressive symptoms within individuals. The entropy baseline levels significantly differed between the two groups (morning: P value < 0.001, Cohen’s d = −2.185; evening: P value < 0.001, Cohen’s d = −1.797) and predicted the recurrence of depressive symptoms, in the current sample. Moreover, higher mean IBIs and Higuchi dimensions were observed in individuals who experienced transitions. While we found little evidence to support the existence of within- individual warning signals in IBI time-series data preceding an upcoming depressive transition, our results indicate that individuals who taper antidepressants and showed lower entropy of cardiac dynamics exhibited a higher chance of recurrence of depression. Hence, entropy could be a potential digital phenotype for assessing the risk of recurrence of depression in the short term while tapering antidepressants