δ15N as an indicator of N2-fixation by cyanobacterial mats in tropical marshes

Cyanobacterial mats (CBM) are important components of wetland ecosystems in limestone-based regions of the Caribbean. During two sampling periods (July 1999 and January 2000) we measured N₂-fixation in samples from 23 different marshes simultaneously with measurements of relevant environmental factors. Samples were evaluated for abundance of five groups of cyanobacteria: (1) Leptolyngbya, (2) Oscillatoria, (3) Chroococcales, (4) Nostoc-& Stigonematales, and (5) dead sheaths. Differences in nitrogen fixation, expressed as nitrogenase activity in nmol C₂H₄ cm^–2 h^–1, were best explained by the proportion of heterocyst-forming cyanobacteria. The samples were analyzed for the natural abundance of ¹⁵N. ¹⁵N values ranged from –1.99 to 11.44 and were strongly negatively correlated with N₂-fixation. With all data included, ¹⁵N was also strongly correlated with nitrates in water. With the samples from Little Belize (high nitrate content marshes) excluded, the effect of nitrate became insignificant. N₂-fixation predicted from ¹⁵N measured on an independent data set from September 2000 was moderately accurate (r² = 0.68, 0.52 and 0.54 for predictions based on July 1999, January 2000 and combined data sets, respectively). When individual sample sets were divided into two groups with ¹⁵N < 2 and ¹⁵N > 2, the two groups were always highly significantly different in terms of their N₂-fixation. The presented evidence suggests that ¹⁵N can be used as a reliable indicator of N₂-fixation by CBM.     

Effect of varying polyglutamate chain length on the structure and stability of ferricytochrome c

The effect of varying polyglutamate chain length on local and global stability of horse heart ferricytochrome c was studied using scanning calorimetry and spectroscopy methods. Spectral data indicate that polyglutamate chain lengths equal or greater than eight monomer units significantly change the apparent pK(a) for the alkaline transition of cytochrome c. The change in pK(a) is comparable to the value when cytochrome c is complexed with cytochrome bc(1). Glutamate and diglutamate do not significantly alter the temperature transition for cleavage of the Met(80)-heme iron bond of cytochrome c. At low ionic strength, polyglutamates consisting of eight or more glutamate monomers increase midpoint of the temperature transition from 57.3+/-0.2 to 66.9+/-0.2 degrees C. On the other hand, the denaturation temperature of cytochrome c decreases from 85.2+/-0.2 to 68.8+/-0.2 degrees C in the presence of polyglutamates with number of glutamate monomers n >or approximately equal 8. The rate constant for cyanide binding to the heme iron of cytochrome c of cytochrome c-polyglutamate complex also decreases by approximately 42.5% with n>or approximately equal 8. The binding constant for the binding of octaglutamate (m.w. approximately 1000) to cyt c was found to be 1.15 x 10(5) M(-1) at pH 8.0 and low ionic strength. The results indicate that the polyglutamate (n>or approximately equal 8) is able to increase the stability of the methionine sulfur-heme iron bond of cytochrome c in spite of structural differences that weaken the overall stability of the cyt c at neutral and slightly alkaline pH.     

Analysis of articulation of fricative praealveolar sibilant "S" in control population

Defective pronunciation of one or more mother language phones, i.e. dyslalia, represents the most frequent speech impairment both in children and adult people. Cases of persisting speech disorder need professional approach and help. The aim of the study was to obtain a model of physiological articulation of the sibilant "s" in children. The method of FFT spectral analysis was made use of. Results will serve for further use in evaluation of speech impairment.     

Extracellular phosphatase activity of natural plankton studied with ELF97 phosphate: fluorescence quantification and labelling kinetics

ELF(R)97 phosphate (ELFP) is a phosphatase substrate which produces ELF(R)97 alcohol (ELFA), a fluorescent water-insoluble product, upon hydrolysis. We studied the kinetics of ELFA precipitation in freshwater samples at levels of total plankton and single phytoplankton cells, and tested the suitability of ELFP for measurement of surface-bound algal extracellular phosphatases. Samples from acidic Plesné Lake (pH approximately 5; high phosphatase activity) and eutrophic Rímov reservoir (pH approximately 7-10; moderate phosphatase activity) were incubated with ELFP for 5-300 min, fixed with HgCl2 and filtered through polycarbonate filters. Relative fluorescence of filter-retained ELFA precipitates was quantified with image analysis. Time-courses of ELFA formation exhibited lag periods followed by finite periods of linear increase. In Plesné Lake, lag-times were shorter (1-18 min) and rates of increase in ELFA fluorescence higher (by approximately 2 orders of magnitude) than in Rímov reservoir (lag-times 30-200 min). Similar patterns of ELFA formation kinetics were also observed in Plesné Lake samples in cuvette spectrofluorometer measurements (which failed in Rímov reservoir). Linear regression of seasonal data on rates of increase in ELFA fluorescence from image cytometry and spectrofluorometry (r2 = 0.65, n = 10) allowed for calibration of image cytometry in terms of amount of cell-associated ELFA. Preliminary measurements of extracellular phosphatase activities of several algae resulted in rates (10-2260 fmol cell-1 h-1) which are comparable to data reported in the literature for algal cultures.     

The contribution of heme propionate groups to the conformational dynamics associated with CO photodissociation from horse heart myoglobin

Photoacoustic calorimetry and transient absorption spectroscopy were used to study conformational dynamics associated with CO photodissociation from horse heart myoglobin (Mb) reconstituted with either Fe protoporphyrin IX dimethylester (FePPDME), Fe octaethylporphyrin (FeOEP), or with native Fe protoporphyrin IX (FePPIX). The volume and enthalpy changes associated with the Fe-CO bond dissociation and formation of a transient deoxyMb intermediate for the reconstituted Mbs were found to be similar to those determined for native Mb (DeltaV1 = -2.5+/-0.6 ml mol(-1) and DeltaH1 = 8.1+/-3.0 kcal mol(-1)). The replacement of FePPIX by FeOEP significantly alters the conformational dynamics associated with CO release from protein. Ligand escape from FeOEP reconstituted Mb was determined to be roughly a factor of two faster (tau=330 ns) relative to native protein (tau=700 ns) and accompanying reaction volume and enthalpy changes were also found to be smaller (DeltaV2 = 5.4+/-2.5 ml mol(-1) and DeltaH2 = 0.7+/-2.2 kcal mol(-1)) than those for native Mb (DeltaV2 = 14.3+/-0.8 ml mol(-1) and DeltaH2 = 7.8+/-3.5 kcal mol(-1)). On the other hand, volume and enthalpy changes for CO release from FePPIX or FePPDME reconstituted Mb were nearly identical to those of the native protein. These results suggest that the hydrogen bonding network between heme propionate groups and nearby amino acid residues likely play an important role in regulating ligand diffusion through protein matrix. Disruption of this network leads to a partially open conformation of protein with less restricted ligand access to the heme binding pocket.     

Relapsed follicular lymphoma sequentially treated with rituximab and 90Y-ibritumomab tiuxetan. Case report

BACKGROUND: Monoclonal antibodies have dramatically changed the treatment possibilities for follicular lymphoma. (90)Y-ibritumomab tiuxetan (Zevalin) is the first radioimmunotherapy agent approved for the treatment of relapsed and resistant follicular lymphoma patients. Long-term benefit was observed especially for patients achieving CR after radioimmunotherapy. METHODS AND RESULTS: A 65-year-old female patient with the second relapse of CD20 positive follicular lymphoma and multiple concomitant diseases was treated with four weekly doses of rituximab (375 mg/m(2)). (18)F-fluoro-deoxyglucose positron emission tomography combined with computed tomography (PET-CT) demonstrated only partial response to therapy with persistent PET scan positivity in enlarged abdominal lymph nodes. Therefore, it was decided to treat her with a 1200-MBq (32-mCi) dose of (90)Y-ibritumomab tiuxetan radioimmunotherapy. No acute complications were noted afterwards. Hematological nadirs were reached 4 weeks later, with a platelet count of 24 x 10(9)/l that normalized within the next 2 weeks. The patient had neither infection nor bleeding complications. Eight weeks after radioimmunotherapy, the PET-CT scans documented only 3 lymph nodes around the abdominal aorta, maximum size 2 x 1 cm. The PET scan analysis proved no accumulation of (18)F-fluoro-deoxy-glucose in any lymph nodes or other organs and tissues. CONCLUSIONS: Sequential treatment with rituximab and (90)Y-ibritumomab tiuxetan may be an interesting alternative in cases of relapsed follicular or other indolent lymphomas in pretreated or older patients with other concomitant diseases.     

Uranium,thorium and rare earth elements in macrofungi: what are the genuine concentrations?

Concentrations of uranium, thorium and rare earth elements (REE) in 36 species of ectomycorrhizal (26 samples) and saprobic (25 samples) macrofungi from unpolluted sites with differing bedrock geochemistry were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Analytical results are supported by use of certified reference materials (BCR-670, BCR-667, NIST-1575a) and the reliability of the determination of uranium was verified by epithermal neutron activation analysis (ENAA). It appears that data recently published on these elements are erroneous, in part because of use of an inappropriate analytical method; and in part because of apparent contamination by soil particles resulting in elevated levels of thorium and REE. Macrofungi from unpolluted areas, in general, did not accumulate high levels of the investigated metals. Concentrations of uranium and thorium were generally below 30 and 125 μg kg⁻¹ (dry weight), respectively. Concentrations of REE in macrofungi did not exceed 360 μg kg⁻¹ (dry weight) and their distribution more or less followed the trend observed in post-Archean shales and loess.     

Backbone assignment and secondary structure of the PsbQ protein from Photosystem II

PsbQ is one of the extrinsic proteins situated on the lumenal surface of photosystem II (PSII) in the higher plants and green algae. Its three-dimensional structure was determined by X-ray crystallography with exception of the residues 14–33. To obtain further details about its structure and potentially its dynamics, we approached the problem by NMR. In this paper we report ¹H, ¹⁵N, and ¹³C NMR assignments for the PsbQ protein. The very challenging oligo-proline stretches could be assigned using ¹³C-detected NMR experiments that enabled the assignments of twelve out of the thirteen proline residues of PsbQ. The identification of PsbQ secondary structure elements on the basis of our NMR data was accomplished with the programs TALOS+, web server CS23D and CS-Rosetta. To obtain additional secondary structure information, three-bond H_N-H_α J-coupling constants and deviation of experimental ¹³C_α and ¹³C_β chemical shifts from random coil values were determined. The resulting “consensus” secondary structure of PsbQ compares very well with the resolved regions of the published X-ray crystallographic structure and gives a first estimate of the structure of the “missing link” (i.e. residues 14–33), which will serve as the basis for the further investigation of the structure, dynamics and interactions.