Cerium and samarium blocked antioxidant enzymes in wheat plants.

This work was conducted to study positive and negative impacts of cerium (Ce) and samarium (Sm) on two cultivars (Arta and Baharan) in wheat plant. Symbols of stress such as proline, malondialdehyde (MDA) and antioxidant enzymes, which may be complicated in the suppression responses of plants, were also studied. Wheat plants were exposed to 0, 2500, 5000, 7500, 10,000 and 15,000 µM of Ce and Sm for 7 days. The growth enhanced in plants treated with lesser Ce and Sm concentration (2500 µM) and declined in plants treated with upper concentrations as compared to untreated plants. The treatment with 2500 µM of Ce and Sm increased dry weigh in Arta by 68.42 and 20% and in Baharan by 32.14% and 27.3%. Thus, Ce and Sm had hormesis effect on growth in wheat plants. According to plant's growth parameter patterns, Arta cultivar had more sensitive to Sm than to Ce, whereas Baharan cultivar had sensitive to Ce than to Sm. Our results indicated impact of Ce and Sm on proline accumulation depended on the dosage of Ce and Sm. It was observed that Ce and Sm accumulated in wheat plants at higher exposure doses. Increment of MDA content by Ce and Sm treatments showed that these metals caused oxidative stress in wheat plants. Ce and Sm blocked enzymatic antioxidant system (superoxide dismutases, peroxidase and polyphenol peroxidase) in wheat. In wheat plants treated with lower Ce and Sm concentrations higher amounts of non-enzymatic antioxidant metabolites were detected. Thus, we showed the potential negative impact of unsuitable utilization of REEs in plants and suggested growth and interruption in physiological and biochemical mechanisms as a possible factor to recognize the underlying toxicological processes.

Fluctuation analysis to select for Samarium bio-uptaking microalgae clones the repurposing of a classical evolution experiment.

Rare Earth Elements (REE) increasing demand prompts the research of biotechnological approaches to exploit secondary resources. We made use of the adapted Fluctuation analyses experiment to obtain Chlamydomonas reinhardtii ChlA strains resistant to Samarium (Sm) as the reference REE. The starting hypothesis was that adaptation to metal-containing media leads to an enhanced metal uptake. ChlA was able to adapt to 1.33·10-4 Sm M and pH~3 by pre-existing genetic variability, allowing the evolutionary rescue of 13 of the 99 populations studied. The rescuing resistant genotypes presented a mutation rate of 8.65·10-7 resistant cells per division. The resulting resistant population contradicted the expected fitness cost associated with the adaptation to Sm, selection resulted in larger and faster-growing resistant cells. Among the three isolated strains studied for Sm uptake, only one presented uplifted performance compared to the control population (46.64 µg Sm g-¹ of wet biomass and 3.26·10-7 ng Sm per cell, mainly bioaccumulated within the cells). The selection of microalgae strains with improved tolerance to REEs by this methodology could be a promising solution for REES sequestration. However, increased tolerance can be independent or have negative effects on uptake performance and cellular features studied are not directly correlated with the metal uptake. SUMMARY SENTENCE: Repurposing a classic laboratory evolution experiment to select for microalgae Samarium adapted strains for metals recovery and biotechnology approaches. DATA AVAILABILITY STATEMENT: All data generated or analyzed during this study are included in this published article (and its raw files).

Comparison of Jordanian and standard diatomaceous earth as an adsorbent for removal of Sm(III) and Nd(III) from aqueous solution.

In this study, Jordanian diatomaceous earth (JDA) and commercial diatomaceous earth (standard diatomaceous earth, SDA) were used for adsorption of samarium (Sm)(III) and neodymium (Nd)(III) ions from aqueous solutions using batch technique as a function of initial concentration of metal ions, adsorbent dosage, ionic strength, initial pH solution, contact time, and temperature. Both adsorbents were characterized by Fourier transform infrared (FTIR), X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller surface area, and cation exchange capacity (CEC). Maximum metal ion uptake was observed after 100 min of agitation, and the uptake has decreased with increasing temperature and reached a maximum at pH ≈ 5. Different types of adsorption isotherms and kinetic models were used to describe the Nd(III) and Sm(III) ion adsorption. The experimental data fitted within the following isotherms in the order Langmuir > Dubinin-Radushkevich (DR) > Freundlich and the pseudo-second-order kinetic model based on their coefficient of determination (R2), chi-square (χ2), and error function (Ferror%) values. Maximum adsorption uptakes, according to the Langmuir model, were obtained as 188.679 mg/g and 185.185 mg/g for Sm(III) and 169.492 mg/g and 149.254 mg/g for Nd(III) by JDA and SDA, respectively. The results of thermodynamic parameters showed that the adsorption of Sm(III) and Nd(III) ions onto JDA and SDA is a feasible, spontaneous, exothermic, and entropy driven. The best recovery for Sm(III) and Nd(III) was obtained when the 0.05 M EDTA + 0.05 M H3PO4 mixture was used as an eluent.

Biosorption of lanthanum and samarium by viable and autoclaved mycelium of Botryosphaeria rhodina MAMB-05.

The ascomycetous fungus, Botryosphaeria rhodina MAMB-05, secretes a (1→3)(1→6)-ß-D-glucan, and the scaled-up production of this ß-glucan results in large amounts of mycelial biomass being produced that represent a potentially cost-effective biosorbent for rare-earth elements. High sorption capacities for both La(III) and Sm(III) were demonstrated for viable and autoclaved lyophilized fungal mycelium. Fourier-transformed infra-red absorption spectra and the point of zero charge (PZC) were similar for the viable and inactive fungal mycelia. The rare-earth lanthanide elements (La and Sm) binding increased at initial pH values greater than 5.0, which was also observed for the PZC determination. The maximum La(III) uptake capacity was observed at lower amounts of La(III) ions in solution, decreasing from 100.0 to 25.3% when the initial lanthanide concentration increased from 15 to 100 mg/L. Lanthanide biosorption by B. rhodina MAMB-05 mycelia followed the Langmuir model, and the affinity of biosorbent functional groups was similar for La(III) and Sm(III).

Response of the freshwater mussel, Dreissena polymorpha to sub-lethal concentrations of samarium and yttrium after chronic exposure.

Samarium (Sm) and yttrium (Y) are commonly used rare earth elements (REEs) but there is a scarcity of information concerning their biological effects in non-target aquatic organisms. The purpose of this study was to determine the bioavailability of those REEs and their toxicity on Dreissena polymorpha after exposure to increasing concentration of Sm and Y for 28 days at 15 °C. At the end of the exposure period, the gene expression of superoxide dismutase (SOD), catalase (CAT), metallothionein (MT), glutathione-S-transferase (GST), cytochrome c oxidase 1 (CO1) and cyclin D (Cyc D) were analysed. In addition, we examined lipid peroxidation (LPO), DNA strand breaks (DSB), GST and prostaglandin cyclooxygenase (COX) activities. Results showed a concentration dependent increase in the level of the REEs accumulated in the soft tissue of mussels. Both REEs decreased CAT but did not significantly modulated SOD and MT expressions. Furthermore, Sm3+ up-regulated GST, CO1 and Cyc D, while Y3+ increased and decreased GST and CO1 transcripts levels, respectively. Biomarker activities showed no oxidative damage as evidenced by LPO, while COX activity was decreased and DNA strand breaks levels were changed suggesting that Sm and Y exhibit anti-inflammatory and genotoxic effects. Factorial analysis revealed that the major impacted biomarkers by Sm were LPO, CAT, CO1 and COX, while GST gene expression, COX, Cyc D and CAT as the major biomarkers affected by Y. We conclude that these REEs display different mode of action but further investigations are required in order to define the exact mechanism involved in their toxicity.

Determination of the speciation and bioavailability of samarium to Chlamydomonas reinhardtii in the presence of natural organic matter.

As technological interest and environmental emissions of the rare earth elements increase, it is becoming more important to assess their potential environmental impact. Samarium (Sm) is a lanthanide of intermediate molar mass that is used in numerous high-technology applications including wind turbines, solar panels, and electric vehicles. The present study relates the speciation of Sm determined in the presence of natural organic matter (NOM) to its bioavailability to the unicellular green alga Chlamydomonas reinhardtii. The free ion concentration was determined using a cation exchange resin (ion exchange technique) in dynamic mode and compared with thermodynamic modeling. Short-term biouptake experiments were performed in the presence of 4 types of NOM: Suwannee River fulvic acids, Pahokee Peat fulvic acids, Suwannee River humic acids, and a Luther Marsh dissolved organic matter isolate (90-95% humic acids). It was clearly shown that even a small amount of NOM (0.5 mg C L-1 ) resulted in a significant decrease (10 times) in the Sm internalization fluxes. Furthermore, complexation with humic acids (and the corresponding reduction in Sm bioavailability) was stronger than that with fulvic acids. The results showed that the experimentally measured (free) Sm was a better predictor of Sm internalization than either the total concentrations or the free ion concentrations obtained using thermodynamic modeling. Environ Toxicol Chem 2018;37:1623-1631. © 2018 SETAC.

MgO:Li,Ce,Sm as a high-sensitivity material for Optically Stimulated Luminescence dosimetry.

The goal of this work was to investigate the relevant dosimetric and luminescent properties of MgO:Li3%,Ce0.03%,Sm0.03%, a newly-developed, high sensitivity Optically Stimulated Luminescence (OSL) material of low effective atomic number (Zeff = 10.8) and potential interest for medical and personal dosimetry. We characterized the thermoluminescence (TL), OSL, radioluminescence (RL), and OSL emission spectrum of this new material and carried out a preliminary investigation on the OSL signal stability. MgO:Li,Ce,Sm has a main TL peak at ~180 °C (at a heating rate of 5 °C/s) associated with Ce(3+) and Sm(3+) emission. The results indicate that the infrared (870 nm) stimulated OSL from MgO:Li,Ce,Sm has suitable properties for dosimetry, including high sensitivity to ionizing radiation (20 times that of Al2O3:C, under the measurement conditions) and wide dynamic range (7 µGy-30 Gy). The OSL associated with Ce(3+) emission is correlated with a dominant, practically isolated peak at 180 °C. Fading of ~15% was observed in the first hour, probably due to shallow traps, followed by subsequent fading of 6-7% over the next 35 days. These properties, together with the characteristically fast luminescence from Ce(3+), make this material also a strong candidate for 2D OSL dose mapping.

Soil-to-plant transfer factors of radioactive Ca, Sm and Pd isotopes: critical assessment of the use of analogies to derive best-estimates from existing non-specific data.

(45)Ca, (151)Sm and (107)Pd are three radionuclides present in low to intermediate in activity radioactive wastes for which no soil-to-plant Transfer Factors (TF) values are available to be used in biosphere models for Ecological Risk Assessment. In the absence of specific radioecological studies, this work reviews and analyzes the existing literature for stable isotopes of Pd, Sm and Ca in order to derive best estimates for TF values that could be used as Transfer Factors. Alternative methods of extrapolation are also critically assessed. The values have been classified according to climatic zone, plant class and soil type for each element. The overall geometric mean TF values (for all plants and conditions) was calculated as 8.4E-02 for Pd, for which the value of radioRu in TRS-472 is also available. The mean TF for Sm was 4.2E-04. This value was lower than the TF values for radioactive Ce that are proposed as alternative values for Sm in TRS-472. The former may be relevant for long term assessments and the latter could possibly used to describe the short term (151)Sm post-release behaviour. The mean value for Ca is 2.3E-01 but varies considerably among plants of a given class due to the variety of plant Ca uptake behaviors. Alternatively, to limit this variability, Ca data content for dry plant matter, as analyzed using the phylogenetic method, could be used to derive TF values if the conservation of isotopic ratio of (45)Ca to stable Ca in soils and in plants hypothesis is taken into account. The TF for Ca in sub-tropical zones is 10-fold lower than in temperate zones. There is a lot of data available about exchangeable Ca in soil, which mean that we could calculate an available TF. The analysis shows that Ca bioavailability is also a key factor within transfer.

Intracellular localization of samarium in the lactating mammary gland cells: ultrastructural and microanalytical study.

The frequent use of some rare earths in the medical and industrial domains make us worry about their intracellular behavior into the body. Reason for which we have investigated the subcellular localization of one of these elements, the samarium, in the mammary gland of lactating female wistar rats using two very sensitive methods of observation and microanalysis, the transmission electron microscopy and the secondary ion mass spectrometry. The ultrastructural study showed the presence of electron dense deposits in the lactating mammary glandular epithelial cell lysosomes of the samarium-treated rats, but no loaded lysosomes were observed in those of control rats. The microanalytical study allowed both the identification of the chemical species present in those deposits as samarium isotopes ((152) Sm(+)) and the cartography of its distribution. Our results confirm the previous ones showing that lysosomes of the glandular epithelial cells are the site of the intracellular concentration of foreign elements such as gallium. The intralysosomal deposits observed in the mammary glandular cells of the samarium-treated rats are similar in their form and density to those observed with the same element in other varieties of cells, such as liver, bone marrow, and spleen cells. Our ultrastructural and microanalytical results and those obtained in previous studies allow deducing that the intralysosomal deposits are very probably composed of an insoluble samarium phosphate salt.

Crystal structures, DNA-binding studies and antioxidant activities of the Ln(III) complexes with 7-methoxychromone- 3-carbaldehyde-isonicotinoyl hydrazone.

The neutral mononuclear Ln(III) complexes (Ln = La, Sm) with 7-methoxychrom-one-3-carbaldehyde-isonicotinoyl hydrazone ligand (L) have been synthesized, characterized and investigated their interactions with calf-thymus DNA. The results show that the binding affinity of the La(III) complex is stronger than that of the Sm(III) complex and that of the ligand (L). Furthermore, the antioxidant activities of the ligand (L) and its Ln(III) complexes (Ln = La, Sm) were studied in detail.

Photoinduced hydroxyl radical and photocatalytic activity of samarium-doped TiO(2) nanocrystalline.

Sm(3+)-doped TiO(2) nanocrystalline has been prepared by sol-gel auto-combustion technique and characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, and also UV-vis diffuse reflectance spectroscopy (DRS). These Sm(3+)-doped TiO(2) samples were tested for methylene blue (MB) decomposition and *OH radical formation. The analysis of *OH radical formation on the sample surface under UV irradiation was performed by fluorescence technique with using terephthalic acid, which readily reacted with *OH radical to produce highly fluorescent product, 2-hydroxyterephthalic acid. It was observed that the presence of Sm(3+) ion as a dopant significantly enhanced the photocatalytic activity for MB degradation under UV light irradiation because both the larger specific surface area and the greater the formation rate of *OH radical were simultaneously obtained for Sm(3+)-doped TiO(2) nanocrystalline. The adsorption experimental demonstrated that Sm(3+)-TiO(2) had a higher MB adsorption capacity than undoped TiO(2) and the adsorption capacity of MB increased with the increase of samarium ion content. The results also indicated that the greater the formation rate of *OH radical was, the higher photocatalytic activity was achieved. In this study, the optimum amount of Sm(3+) doping was 0.5 mol%, at which the recombination of photo-induced electrons and holes could be effectively inhibited, the highest formation rate of *OH radicals was, and thereby the highest photocatalytic activity was achieved.

Targeting of lanthanide(III) chelates of DOTA-type glycoconjugates to the hepatic asyaloglycoprotein receptor: cell internalization and animal imaging studies.

The characterization of a new class of hydrophilic liver-targeted agents for gamma-scintigraphy and MRI, consisting, respectively, of [(153)Sm](3+) or Gd(3+) complexes of DOTA monoamide or bisamide linked glycoconjugates (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), is reported. In vitro studies show high uptake of radiolabeled [(153)Sm]-DOTAGal(2) by the human hepatocyte carcinoma cell line Hep G2 containing the asialoglycoprotein receptor (ASGP-R), which is decreased to less than 50% by the presence of its high-affinity ligand asialofetuin (ASF). In vivo biodistribution, gamma-imaging and pharmacokinetic studies on Wistar rats using the [(153)Sm](3+)-labeled glycoconjugates show a high uptake in the receptor-rich organ liver of the radiolabeled compounds containing terminal galactosyl groups, but very little uptake for those compounds with terminal glycosyl groups. Blocking the receptor in vivo reduced liver uptake by 90%, strongly suggesting that the liver uptake of these compounds is mediated by their binding to the asyaloglycoprotein receptor (ASGP-R). This study also demonstrated that the valency increase improves the targeting capability of the glycoconjugates, which is also affected by their topology. However despite the specific liver uptake of the radiolabeled galactose-bearing multivalent compounds, the animal MRI assessment of the corresponding Gd(3+) chelates shows liver-to-kidney contrast effects which are not significantly better than those shown by GdDTPA. This probably results from the quick wash-out from the liver of these highly hydrophilic complexes, before they can be sufficiently concentrated within the hepatocytes via receptor-mediated endocytosis.

Extension to 2268 atoms of direct methods in the ab initio determination of the unknown structure of bacteriophage P22 lysozyme.

The X-ray crystal structure of the previously unknown bacteriophage P22 lysozyme, the product of gene 19, has been determined ab initio by direct methods using the program SIR2002. The presence of several partially occupied iodine anions and samarium cations augmented the ability of direct methods to locate all 2268 non-H protein atoms in the asymmetric unit, making this one of the largest structures to date to be determined ab initio. The iodides were introduced from a quick soak, which the crystal survived sufficiently well to diffract to 1.04 angstroms resolution. The complete heavy-atom substructure contributed 6.6% of the total scattering power. The initial determination of the structure assumed that there were two iodide ions in the asymmetric unit, although it was later determined that these sites correspond to partially occupied samarium ions. Tests suggested that it is better to overestimate rather than underestimate the heavy-atom content. While experimental phases from all of the successful tests were of high quality, the best results came from a SAD experiment using the programs SHELXD and SHELXE. Nonetheless, ab initio structure determination by direct methods was found to be a viable alternative to traditional protein crystallographic methods provided that the X-ray data extend to atomic resolution and heavy atoms with sufficient scattering power are present in the crystal.

High-resolution crystal structure of manganese peroxidase: substrate and inhibitor complexes.

Manganese peroxidase (MnP) is an extracellular heme enzyme that catalyzes the peroxide-dependent oxidation of Mn(II) to Mn(III). The Mn(III) is released from the enzyme in complex with oxalate. One heme propionate and the side chains of Glu35, Glu39, and Asp179 were identified as Mn(II) ligands in the 2.0 A resolution crystal structure. The new 1.45 A crystal structure of MnP complexed with Mn(II) provides a more accurate view of the Mn-binding site. New features include possible partial protonation of Glu39 in the Mn-binding site and glycosylation at Ser336. This is also the first report of MnP-inhibitor complex structures. At the Mn-binding site, divalent Cd(II) exhibits octahedral, hexacoordinate ligation geometry similar to that of Mn(II). Cd(II) also binds to a putative second weak metal-binding site with tetrahedral geometry at the C-terminus of the protein. Unlike that for Mn(II) and Cd(II), coordination of trivalent Sm(III) at the Mn-binding site is octacoordinate. Sm(III) was removed from a MnP-Sm(III) crystal by soaking the crystal in oxalate and then reintroduced into the binding site. Thus, direct comparisons of Sm(III)-bound and metal-free structures were made using the same crystal. No ternary complex was observed upon incubation with oxalate. The reversible binding of Sm(III) may be a useful model for the reversible binding of Mn(III) to the enzyme, which is too unstable to allow similar examination.

Avidin-biotin system pretargeting radioimmunoimaging and radioimmunotherapy and its application in mouse model of human colon carcinoma.

AIM: To evaluate the multi-step pretargeting radioimmunoimaging (RII) and radioimmunotherapy (RIT) in nude mice bearing human colon carcinoma with avidin-biotin system labeled with (153)Sm. METHODS: Two- and three-step strategies for avidin-biotin system pretargeting techniques were established. In a three-step procedure, human colon carcinoma bearing nude mice were first injected with biotinylated monoclonal antibody (McAb-Bt) followed by cold avidin (Av) 48 h later and then (153)Sm-DB(2) 24 h thereafter; whereas the two-step procedure consisted of injection of (153)Sm-SA 48 h after pretargeting with biotinylated anti-CEA monoclonal antibody (CEA McAb-Bt). SPECT imaging and biodistribution were performed at 4, 24, 48, or 72 h after injection of (153)Sm-labeled compounds. Five groups of nude mice subcutaneously grafted with human colon carcinoma were treated 3 d after grafting. One group received the injection with 100 microg CEA McAb-Bt followed by cold avidin (80 microg) after 2 d and 11.1 MBq (153)Sm-DB(2) after 1 d. Four control groups were treated respectively with 11.1 MBq (153)Sm-CEA McAb, 11.1 MBq (153)Sm-nmIgG, 11.1 MBq (153)Sm-DB(2), 100 microL normal saline. Toxicity was evaluated by changes of leukocyte count, and the efficacy by variation in tumor volume. Histological analyses of tumors were performed. RESULTS: The three-step procedure allowed faster blood clearance and yielded higher tumor blood ratios (5.76 at 4 h and 12.94 at 24 h) of the (153)Sm-DB(2). The tumor was clearly visualized at 4 h in gamma-imaging after the injection of (153)Sm-DB(2), while a significant accumulation of (153)Sm-SA in the tumor was observed only 24 h after the injection and tumor blood ratios at 4 and 24 h were 1.00 and 2.03, respectively, in the two-step procedure. Pretargeting RIT and (153)Sm-CEA McAb had a strong tumor-inhibiting effect. The tumor inhibitory rate was 80.67% and 78.44%, respectively, five weeks after therapy. Histopathological evidence also indicated radioactive damage in tumor tissues as necrosis of tumor cells, while in the other organs such as liver and kidney no radioactive damage was observed. Leukocyte counts showed significant decrease after treatment in groups of (153)Sm-CEA McAb and (153)Sm-nmIgG. CONCLUSION: The two kinds of pretargeting strategies can elevate the target-to-nontarget ratio, decrease the blood background and shorten the imaging time compared to (153)Sm-CEA McAb. Three-step pretargeting RIT is as efficient as (153)Sm-CEA McAb, but markedly less toxic. This study provides experimental evidence for the clinical application of pretargeting RII and RIT.

The first directed reduction of beta-alkoxy ketones to anti-1,3-diol monoethers: identification of spectator and director alkoxy groups.

A new reduction procedure for the stereoselective reduction of certain beta-alkoxy ketones is described. The method relies upon electron-transfer reduction using samarium diiodide in THF with MeOH as an additive. Reduction is facile for a number of alkoxy groups that can complex samarium effectively but is not observed with TBS or benzyl protecting groups. Experiments with deuterated methanol show that the stereoselectivity arises from protonation of a samarium carbanion intermediate.

Rare earth elements as nonabsorbable fecal markers in studies of iron absorption.

The use of rare earth elements as nonabsorbable fecal markers for studies of iron absorption from sources labeled extrinsically with stable isotopes was evaluated. On 3 successive days 13 healthy fasting adults were given different stable isotopes of iron with samarium, ytterbium, or dysprosium. On day 1, three meals were given with 57Fe (1 mg per meal) plus samarium (0.33 mg per meal); on day 2, identical meals (taken with a calcium supplement to reduce iron bioavailability) were given with equivalent amounts of 58Fe-labeled iron and ytterbium; on day 3, a well-absorbed reference dose of 54Fe (3 mg) was given with 1 mg Dy. A complete fecal collection was carried out for 5-9 d and each stool was analyzed for rare earth elements by inductively coupled plasma-mass spectrometry and iron isotopes by thermal ionization quadrupole mass spectrometry. Mean recovery of rare earth elements was 101%, indicating that they are totally unabsorbed. The excretory pattern of the iron isotopes and the rare earth elements was very similar; the correlation coefficients between samarium and 57Fe, ytterbium and 58Fe, and dysprosium and 54Fe were 0.992, 0.989, and 0.988, respectively (P < 0.001). Iron absorption was calculated as the difference between isotope dose and fecal excretion. Mean (+/-SEM) iron absorption was 16.7 +/- 2.4%, 4.3 +/- 1.6%, and 40.3 +/- 3.1% on days 1-3, respectively. Predicted values estimated from the first 4 d of pooled feces, using the rare earth element recovery data to produce corrected figures for unabsorbed isotope, were in close agreement: 19.1 +/- 2.1%, 4.6 +/- 1.7%, and 40.8 +/- 3.1%, respectively (P < 0.001). With the diet of medium iron bioavailability and with the highly bioavailable reference dose it was possible to predict iron absorption accurately from only one or two stools, provided that they were sufficiently enriched with isotope and a rare earth element.

C2 domain conformational changes in phospholipase C-delta 1.

The structure of the PH-domain truncated core of rat phosphoinositide-specific phospholipase C-delta 1 has been determined at 2.4 A resolution and compared to the structure previously determined in a different crystal form. The stereochemical relationship between the EF, catalytic, and C2 domains is essentially identical. The Ca2+ analogue Sm3+ binds at two sites between the jaws of the C2 domain. Sm3+ binding ejects three lysine residues which bridge the gap between the jaws and occupy the Ca2+ site in the apoenzyme, triggering a conformational change in the jaws. The distal sections of the C2 jaws move apart, opening the mouth by 9 A and creating a gap large enough to bind a phospholipid headgroup.

X-ray studies reveal lanthanide binding sites at the A/B5 interface of E. coli heat labile enterotoxin.

The crystal structure determination of heat labile enterotoxin (LT) bound to two different lanthanide ions, erbium and samarium, revealed two distinct ion binding sites in the interface of the A subunit and the B pentamer of the toxin. One of the interface sites is conserved in the very similar cholera toxin sequence. These sites may be potential calcium binding sites. Erbium and samarium binding causes a change in the structure of LT: a rotation of the A1 subunit of up to two degrees relative to the B pentamer.

Labeling of monoclonal antibodies with samarium-153 for combined radioimmunoscintigraphy and radioimmunotherapy.

The labeling of a monoclonal antibody K-1-21 with 153Sm has been investigated using the bifunctional chelate cyclic diethylenetriaminepentaacetic acid (DTPA) anhydride. Labeling efficiencies greater than 60% were obtained using high specific activity [153Sm]chloride and a cDTPAa:MAb conjugation ratio of 20:1. The resultant labeled antibody had a s.a. greater than 150 MBq.mg-1 and a % retained immunoreactivity greater than 90%. Imaging and biodistribution studies in a rat model demonstrated that specific uptake of 153Sm-K-1-21 into s.c. implants of the target antigen could be clearly detected in scintigrams at 6 days p.i. The specific uptake (1.90 +/- 0.45% ID/g, 19.95 +/- 2.20 Implant:Blood ratio) compared favorably to 131I- and 111In-labeled K-1-21 (2.52 +/- 0.20 and 3.33 +/- 0.20% ID/g, 7.69 +/- 0.45 and 10.10 +/- 0.60 I:B, respectively). Labeling of MAbs with 153Sm for combined scintigraphy/therapy is feasible at clinically appropriate specific activities using cDTPAa, with the resultant conjugates retaining immunoreactivity and in vivo antigen localization.