Structure and orientation of the Mn4Ca cluster in plant photosystem II membranes studied by polarized range-extended x-ray absorption spectroscopy

X-ray absorption spectroscopy has provided important insights into the structure and function of the Mn(4)Ca cluster in the oxygen-evolving complex of Photosystem II (PS II). The range of manganese extended x-ray absorption fine structure data collected from PS II until now has been, however, limited by the presence of iron in PS II. Using a crystal spectrometer with high energy resolution to detect solely the manganese Kalpha fluorescence, we are able to extend the extended x-ray absorption fine structure range beyond the onset of the iron absorption edge. This results in improvement in resolution of the manganese-backscatterer distances in PS II from 0.14 to 0.09A(.) The high resolution data obtained from oriented spinach PS II membranes in the S(1) state show that there are three di-mu-oxo-bridged manganese-manganese distances of approximately 2.7 and approximately 2.8A in a 2:1 ratio and that these three manganese-manganese vectors are aligned at an average orientation of approximately 60 degrees relative to the membrane normal. Furthermore, we are able to observe the separation of the Fourier peaks corresponding to the approximately 3.2A manganese-manganese and the approximately 3.4A manganese-calcium interactions in oriented PS II samples and determine their orientation relative to the membrane normal. The average of the manganese-calcium vectors at approximately 3.4A is aligned along the membrane normal, while the approximately 3.2A manganese-manganese vector is oriented near the membrane plane. A comparison of this structural information with the proposed Mn(4)Ca cluster models based on spectroscopic and diffraction data provides input for refining and selecting among these models.     

Thomas John Wydrzynski (8 July 1947–16 March 2018)

Photosynthesis Research - With this Tribute, we remember and honor Thomas John (Tom) Wydrzynski. Tom was a highly innovative, independent and committed researcher, who had, early in his career,...     

Downregulation of calcineurin activity in cervical carcinoma

Background  

Calcineurin (CaN) is an important serine-threonine phosphatase (PP2B), which plays a crucial role in calcium-calmodulin mediated signal transduction events. Calcineurin has been implicated in pathogenesis of various diseases cardiac hypertrophy, diabetic neuropathy and Alzheimer's, however its role in neoplasia remains unclear.     

A cetylated fatty acid topical cream with menthol reduces pain and improves functional performance in individuals with arthritis

This investigation was an extension of a previous study conducted in our laboratory in which we showed that 1 month of treatment with a topical cream (Celadrin) consisting of cetylated fatty acids was effective for reducing pain and improving functional performance in individuals with osteoarthritis (OA) of the knee (Kraemer et al., Journal of Rheumatology, 2004). We wanted to verify that the addition of menthol to the compound would produce a similar percentage of improvement in therapeutic effects. We used a single treatment group with a pre-post experimental design to examine % treatment changes. Individuals diagnosed with OA of the knee (N = 10; age, 66.4 +/- 11.5 years) and severe pain (e.g., OA, rheumatoid arthritis) of the elbow (N = 8; age, 59.1 +/- 18.2 years) and wrist (N = 10; age, 60.3 +/- 16.8 years) were tested for pain and functional performance before and after 1 week of treatment with a topical cream consisting of cetylated fatty acids and menthol applied twice per day. In individuals with knee OA, significant improvements in stair-climbing ability (about 12%), "up-and-go" performance (about 12%), balance and strength (about 16.5%), and range of motion (about 3.5%) were observed, as were reductions in pain. In individuals with severe pain of the elbow and wrist, significant improvements in dynamic (about 22 and 24.5%, respectively) and isometric (about 33 and 42%, respectively) local muscular endurance were observed, as was a reduction in pain. Neither group demonstrated significant changes in maximal grip strength or maximal force production. One week of treatment with a topical cream consisting of cetylated fatty acids and menthol was similarly effective for reducing pain and improving functional performance in individuals with arthritis of the knee, elbow, and wrist. The % changes were consistent with our prior work on the compound without menthol. Further work is needed to determine the impact of menthol in such a cream. Nevertheless, our data support the use of a topical cream consisting of cetylated fatty acids (with or without menthol) for enhancing the potential for exercise training in this population.     

Use of Old World monkeys for acquired immunodeficiency syndrome research

Mangabeys, macaques, and baboons persistently infected with human immunodeficiency virus (HIV)-2 NIH-DZ demonstrated no signs of immunodeficiency disease after 6-11 months following seroconversion. Thus Old World monkeys provide an animal model to investigate the effects of passive immunization (anti-HIV-2 antibodies) on HIV infection in primates.     

The reactivity of hydrazine with photosystem II strongly depends on the redox state of the water oxidizing system

The decay kinetics of the redox states S2 and S3 of the water-oxidizing enzyme have been analyzed in isolated spinach thylakoids in the absence and presence of the exogenous reductant hydrazine. In control samples without NH2NH2 a biphasic decay is observed. The rapid decline of S2 and S3 with YD as reductant exhibits practically the same kinetics with t1/2 = 6-7 s at pH = 7.2 and 7 degrees C. The slow reduction (order of 5-10 min at 7 degrees C) of S2 and S3 with endogenous electron donors other than YD is about twice as fast for S2 as for S3 under these conditions. In contrast, the hydrazine-induced reductive shifts of the formal redox states Si (i = 0...3) are characterized by a totally different kinetic pattern: (a) at 1 mM NH2NH2 and incubation on ice the decay of S2 is estimated to be at least 25 times faster (t1/2 less than or equal to 0.4 min) than the corresponding reaction of S3 (t1/2 approximately 13 min); (b) the NH2NH2-induced decay of S3 is even slower (about twice) than the transformation of S1 into the formal redox state 'S-1' (t1/2 approximately 6 min), which gives rise to the two-digit phase shift of the oxygen-yield pattern induced by a flash train in dark adapted thylakoids. (c) the NH2NH2-induced transformation S0----'S-2' [Renger, Messinger and Hanssum (1990) in: Curr.' Res. Photosynth. (Baltscheffsky, M., ed), Vol. 1, pp. 845-848, Kluwer, Dordrecht] is about three times faster (t1/2 approximately 2 min) than the reaction [see text]. Based on these results, the following dependence on the redox state Si of the reactivity towards NH2NH2 is obtained: S3 less than S1 less than S0 much less than S2. The implications of this surprising order of reactivity are discussed.     

Neural correlates of knowledge: stable representation of stimulus associations across variations in behavioral performance

Behavioral responses to a sensory stimulus are often guided by associative memories. These associations remain intact even when other factors determine behavior. The substrates of associative memory should therefore be identifiable by neuronal responses that are independent of behavioral choices. We tested this hypothesis using a paired-associates task in which monkeys learned arbitrary associations between pairs of visual stimuli. We examined the activity of neurons in inferior temporal cortex as the animals prepared to choose a remembered stimulus from a visual display. The activity of some neurons (22%) depended on the monkey's behavioral choice; but for a novel class of neurons (54%), activity reflected the stimulus that the monkey was instructed to choose, regardless of the behavioral response. These neurons appear to represent memorized stimulus associations that are stable across variations in behavioral performance. In addition, many neurons (74%) were modulated by the spatial arrangement of the stimuli in the display.     

Evidence that bicarbonate is not the substrate in photosynthetic oxygen evolution

It is widely accepted that the oxygen produced by photosystem II of cyanobacteria, algae, and plants is derived from water. Earlier proposals that bicarbonate may serve as substrate or catalytic intermediate are almost forgotten, though not rigorously disproved. These latter proposals imply that CO2 is an intermediate product of oxygen production in addition to O2. In this work, we investigated this possible role of exchangeable HCO3- in oxygen evolution in two independent ways. (1) We studied a possible product inhibition of the electron transfer into the catalytic Mn4Ca complex during the oxygen-evolving reaction by greatly increasing the pressure of CO2. This was monitored by absorption transients in the near UV. We found that a 3,000-fold increase of the CO2 pressure over ambient conditions did not affect the UV transient, whereas the S(3) --> S(4) --> S(0) transition was half-inhibited by raising the O2 pressure only 10-fold over ambient, as previously established. (2) The flash-induced O2 and CO2 production by photosystem II was followed simultaneously with membrane inlet mass spectrometry under approximately 15% H2(18)O enrichment. Light flashes that revealed the known oscillatory O2 release failed to produce any oscillatory CO2 signal. Both types of results exclude that exchangeable bicarbonate is the substrate for (and CO2 an intermediate product of) oxygen evolution by photosynthesis. The possibility that a tightly bound carbonate or bicarbonate is a cofactor of photosynthetic water oxidation has remained.     

Ribes (Grossulariaceae) phylogeny as indicated by restriction-site polymorphisms of PCR-amplified chloroplast DNA

We surveyed exemplars from all 12 infrageneric taxa ofRibes (Grossulariaceae) for restriction site variation in two cpDNA regions, fromrbcL toaccD and fromrpoC1 torpoC2, in order to develop an explicit phylogenetic hypothesis and to assess the validity of infrageneric classifications. Maximum parsimony analysis resolves sect.Ribes (red currants), sect.Berisia (European alpine currants), sect.Symphocalyx (golden currants), sect.Grossularia plus sect.Grossularioides (true gooseberries and spiny currants), andHesperia, Lobbia, and probably sect.Robsonia (west North American gooseberries) as well-supported monophyletic groups. The clade of sectionsGrossularioides andGrossularia is unexpected, and suggests that subgenusGrossularia is not monophyletic. Alternatively, sect.Grossularioides may have acquired its cpDNA via hybridization and introgression. SectionsCoreosma (black currants) andHeritiera (dwarf currants) are apparently non monophyletic. Relationships among the well-supported lineages and the other sampled taxa remain unresolved. Maximum likelihood analysis is consistent with the parsimony results.