The fate of P2Y-related orphan receptors: GPR80/99 and GPR91 are receptors of dicarboxylic acids

Several orphan G protein-coupled receptors are structurally close to the family of P2Y nucleotide receptors: GPR80/99 and GPR91 are close to P2Y_1/2/4/6/11 receptors, whereas GPR87, H963 and GPR34 are close to P2Y_12/13/14. Over the years, several laboratories have attempted without success to identify the ligands of those receptors. In early 2004, two papers have been published: One claiming that GPR80/99 is an AMP receptor, called P2Y₁₅, and the other one showing that GPR80/99 is a receptor for -ketoglutarate, while GPR91 is a succinate receptor. The accompanying paper by Qi et al. entirely supports that GPR80/99 is an -ketoglutarate receptor and not an AMP receptor. The closeness of dicarboxylic acid and P2Y nucleotide receptors might be linked to the negative charges of both types of ligands and the involvement of conserved Arg residues in their neutralization.     

A knowledge-based three dimensional model of the Photosystem II reaction center of Chlamydomonas reinhardtii

In this Minireview, a comparison of the binding niches of the PS II cofactors from several existing models of the PS II reaction center is provided. In particular, it discusses a three dimensional model of the Photosystem II (PS II) reaction center including D1, D2 and cytochrome b559 proteins from the green alga Chlamydomonas reinhardtii that was specifically generated for this Minireview. This model is the most complete to date and includes accessory chlorophyll_zs, a manganese cluster, two molecules of -carotene and cytochrome b559, all of which are essential components of the PS II reaction center. The modeling of the D1 and D2 proteins was primarily based on homology with the L and M subunits of the anoxygenic purple bacterial photosynthetic reaction centers. The non-homologous loop regions were built using a sequence specific approach by searching for the best-matched protein segments in the Protein Data Bank, and by imposing the matching conformations on the corresponding D1 and D2 regions. Cytochrome b559 which is in close proximity to D1 and D2 was tentatively modeled in / conformation and docked on the Q_B side of the PS II reaction center according to experimental suggestions. An alternate docking on the Q_A side is also shown for comparison. The cofactors in the PS II reaction center were modeled either by adopting the structures from the bacterial counterparts, when available, with modifications based on existing experimental data or by de novo modeling and docking in the most probable positions in the reaction center complex. The specific features of this model are the inclusion of the tetramanganese cluster (with calcium and chloride ions) in a open, C-shaped structure modeled within the D1/D2/cytochrome b559 complex with D1-D170, D1-E189, D1-D342 and D1-A344 as putative ligands; and the modeling of two cis -carotenes and two accessory chlorophyll_zs liganded by D1-H118 and D2-H117. We also analyzed residues in the model which may be involved in the D1 and D2 inter-protein interactions, as well as residues which may be involved in putative bicarbonate and water binding and transport.     

Calcium-induced compaction and its inhibition in embryonal carcinoma cell aggregates

H6 embryonal carcinoma cells form aggregates of cells in culture medium which contains 2 mM calcium. These aggregates are described as uncompacted, indicating that the individual cells of the aggregate are spherical and are in limited contact with each other. In contrast, compaction of the aggregate, induced by increasing the calcium concentration, results in a tight mass of cells flattened against one another and connected by intercellular junctions. At least 85-97% of the aggregates undergo compaction in 7 mM calcium and are subsequently decompacted if removed to 2 mM calcium. Since calcium ionophore A23187 does not induce compaction, extracellular rather than intracellular calcium seems to be the limiting factor. We have demonstrated that this calcium-induced morphogenetic change is sensitive to inhibition by agents which also prevent the calcium-dependent compaction of the 8-cell mouse embryo. The cytoskeletal-binding drugs tetracaine HCl, colcemid, vinblastine, colchicine, and cytochalasin B each inhibit compaction of H6 aggregates. Interference at surface molecule sites by exposure to the lectins wheat germ agglutinin or concanavalin A or by interruption of glycosylation with exposure to tunicamycin, or by reaction with anti-H6 Fab or anti-F9, also prevent compaction. Since the mouse embryo and embryonal carcinoma cells share certain processes which are involved in initiating and maintaining compaction, these processes and their subsequent roles in differentiation may be examined using embryonal carcinoma cell aggregates.     

640 层CT 对肝癌碘油栓塞沉积不良的临床分析

目的:探讨640层CT对肝癌碘油栓塞沉积不良患者治疗方案的临床指导。方法:21例富血供肝癌碘油动脉栓塞后,复查肝脏CT病灶内碘油沉积不良患者,用640层螺旋CT行CT灌注成像、CT动脉成像检查。结果:21例碘油沉积不良病灶内仍有动脉血供18例,坏死3例,18例有动脉血供病灶由肝动脉供血6例,膈下动脉供血3例,肠系膜上动脉供血4例,右侧副肾动脉供血1例,胃左动脉供血2例,右肾动脉供血2例。结论:640层螺旋CT灌注成像、CT动脉成像,可以准确显示肿瘤病灶碘油栓塞后肿瘤的残留与坏死,特别能精确判断肿瘤病灶血供起源情况,对再次介入治疗具有重要价值。     

A simple method for detecting steroid aggregation and estimating solubility in aqueous solutions

Steroids are generally sparingly soluble in water. Thus, for in vitro studies of steroid metabolism or enzymology it is common practice to solubilize steroids by the addition of a small amount (2–10%, v/v) of an organic cosolvent. Methanol, ethanol, and 1,2-propanediol, singly or in combination, have been widely used (1). Effects of organic solvents on the kinetic parameters, K_m and V_max, of steroid-metabolizing enzymes with various substrates have been demonstrated (2,3), and the results are consistent with the conclusion that organic solvent influences on catalytic activity reflect, in part, effects on the aggregation state and solubility of steroid substrates.Light-scattering measurements have been applied extensively in studies of macromolecular structure (4) and micelle formation by a large variety of amphiphilic substances [reviewed in Ref. (5)]. Jones and Gordon (6) used a commercial instrument, designed specifically for light-scattering measurements, to characterize micelle formation in aqueous solutions by Δ5-3-ketosteroids containing various substituents at the 17β position. They showed that turbidity versus concentration plots were of the form seen in studies of micelle formation (5) and that steroids can exist in solution in monomeric or micellar forms, their aggregation state being a function of the polarity of the steroid solute and the composition of the solvent.To estimate solubility quantitatively ³H- or ¹⁴C-labeled steroids have been used in conjunction with centrifugation (3), dialysis (7), or filtration (8). These techniques allow for accurate estimates of solubility, but one may encounter problems due to nonspecific absorption on membranes or the unavailability of the labeled steroid of interest.We have observed that steroid aggregation and solubility can be estimated easily and with high sensitivity with a commercially available fluorometer. In this report the method is described and examples demonstrating the reproducibility and sensitivity of the technique are presented.