A comparative study on physicochemical properties of hydroxyapatite powders derived from natural and synthetic sources

Hydroxy apatite (HA) is effectively used as a bioimplant material because it closely resembles bone apatite and exhibits good biocompatibility. So, in this research, HA powders were produced by calcinations of natural bones including human, bovine, camel and horse bones, and also via sol-gel method. Powders characterizations of natural HA and Synthetic HA were studied by X-ray powder diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM), combined with transmission electron microscopy (ТЕМ). In order to verify the biocompatibility of these HA powders, MTT assay was applied. The XRD results showed that the HA powders were successfully produced by using different sources. Also, it was obvious from XRF analysis that the main components of them were Ca and P. Furthermore, it was seen that the size of particles was in the nanometric scale and they showed agglomerates consisting of numerous nanocrystals. FTIR spectra of all samples proved the presence of various CO ₃ ^2- , PO ₄ ^3- and OH^– groups in the powders. In addition, the MTT assay revealed that the cells proliferations in the presence of horse and human HA nanopowders were stimulated.     

镁铝复合氧化物的固相反应热力学计算及固相合成研究

采用固相法合成镁铝氧化物,通过固相反应的热力学计算得到临界温度值,并通过热重曲线分析反应的中间过程。加入AlF3参与到矿石固相合成反应中,通过XRD观察发现,AlF3能有效降低矿石固相合成温度近200℃,还起到助熔剂的作用。     

Delineation of two functionally distinct gammaPDE binding sites on the bovine retinal cGMP phosphodiesterase by a mutant gammaPDE subunit

The gamma subunit of the retinal cGMP phosphodiesterase (gammaPDE) acts as an inhibitor of phosphodiesterase (PDE) catalytic activity and mediates enzyme regulation by the alpha subunit of the GTP-binding protein transducin (alphaT). In this work, we describe a full length, doubly point-mutated gamma subunit, C68S, Y84C gammaPDE, which binds to PDE with increased affinity but has a decreased ability to inhibit the enzyme. Fluorescence studies monitoring the competition between wild-type gammaPDE and the C68S, Y84C gammaPDE mutant suggest that the mutant gammaPDE binds with high affinity to only half of the total sites occupied by wild-type gammaPDE. Competition studies between wild-type gammaPDE and the mutant further suggest that the wild-type protein is able to fully inhibit PDE activity even when the mutant gammaPDE occupies its high-affinity binding site on PDE. Taken together, our findings are consistent with a model in which there are two distinguishable binding sites for gammaPDE on the PDE enzyme but that only one of the two sites mediates PDE inhibition.     

Solid phase bovine thrombin. Preparation and properties

A new solid-phase thrombin (EC 3.4.21.5) was prepared through conjugation of the enzyme under mild conditions to a glass support bearing an active ester of N-hydroxysuccinimide. The immobilized enzyme retained 50 +/- 10% of the specific esterase activity of the parent soluble enzyme. The Km (apparent) for the esterase activity of the immobilized enzyme has a value of 5 mM, identical of the Km value of the parent-soluble enzyme. Only 6 +/- 1% of the specific proteolytic activity was retained and a higher Km (apparent) value of 67 muM was obtained for the insoluble enzyme compared to Km value of 12.5 muM for the parent soluble thrombin. Solid-phase thrombin prepared by the diazocoupling technique was previously reported to retain only 3% of the specific proteolytic activity. The observed loss of specific proteolytic activity can be attributed to steric interference, a change in charge characteristics, or both. Nevertheless, the present method of preparation has the advantages of rapidity and simplicity. It can readily be adapted to use for studying the fate of various complexes of fibrinogen, fibrin and their degradation products. It should also be useful for preparing radiolabeled autologous soluble fibrin for thrombus detection in patients undergoing active thrombosis.     

Parallel synthesis and screening of a solid phase carbohydrate library

A solid phase carbohydrate library was synthesized and screened against Bauhinia purpurea lectin. The library, which contains approximately 1300 di- and trisaccharides, was synthesized with chemical encoding on TentaGel resin so that each bead contained a single carbohydrate. Two ligands that bind more tightly to the lectin than Gal-beta-1,3-GalNAc (the known ligand) have been identified. The strategy outlined can be used to identify carbohydrate-based ligands for any receptor; however, because the derivatized beads mimic the polyvalent presentation of cell surface carbohydrates, the screen may prove especially valuable for discovering new compounds that bind to proteins participating in cell adhesion.     

Purification and characterization of a troponin C-like phosphodiesterase activator from bovine thyroid

A troponin C-like phosphodiesterase activator from bovine thyroid has been purified to homogeneity. The overall purification was about 9,800-fold with a yield of 8%. Bovine thyroid activator protein is identical in biologic properties to that isolated from bovine brain. They have the same specific activity regarding stimulation of bovine brain cyclic nucleotide phosphodiesterase. Both proteins form a Ca2+-dependent complex with heart muscle troponin I which is stable in 6M urea-polyacrylamide gel and which is similar, but not identical, to the troponin C-troponin I complex. The physiochemical properties of bovine thyroid activator protein are identical with those of bovine brain and other phosphodiesterase activator proteins and are similar to heart muscle and skeletal muscle troponin C as follows: (A) they bind 3-4 exchangeable calcium ions/mol with dissociation constants between 10(-5) and 10(-6) M, (B) they are highly acidic with a high content of aspartic and glutamic acids and isoelectric points of approximately 4.1, (C) these proteins have an unusual ultraviolet absorption spectrum with six discrete maxima between 250 and 284 nm which are characteristic of phenylalanine and tyrosine, and (D) these proteins have a low content of cysteine, histidine, tyrosine and proline. The tryptic peptide maps of bovine thyroid and brain activator protein are very similar. However, despite a very similar amino acid composition, the peptide map of bovine heart muscle troponin C is significantly different from that of the other two proteins. The molecular weight of thyroid and brain activator protein is 16,500, while that of heart troponin C is 18,500. Thyroid and brain activator protein, as well as heart troponin C, appear to undergo significant Ca2+-dependent conformational changes, as measured by the difference in the circular dichroism spectrum and electrophoretic mobility observed in the presence and absence of calcium ion.     

Monitoring of solid phase peptide synthesis by FT-IR spectroscopy

Aggregation phenomena of growing peptides on the resin have seldom been investigated. We report here how conformations are determined by FT-IR spectroscopy. Therefore the sequence 80-99 of HIV 1-protease was synthesized. After every coupling a resin sample was taken out of the reaction column and a FT-IR spectrum recorded. The results were compared with the UV monitoring obtained from another synthesis of the same peptide.     

The prediction and representation of phase equilibria and physicochemical properties in complex slag systems

The development of new experimental techniques for the determination of phase equilibria in complex slag systems, chemical thermodynamic, and viscosity models is reported. The new experimental data, and new thermodynamic and viscosity models, have been combined in a custom-designed computer software package to produce limiting operability diagrams for slag systems. These diagrams are used to describe phase equilibria and physicochemical properties in complex slag systems. The approach is illustrated with calculations on the system FeO-Fe₂O₃-CaO-SiO₂-Al₂O₃ at metallic iron saturation, slags produced in coal slagging gasifiers, and in the reprocessing of nonferrous smelting slags. This article was presented at the Mills Symposium “Molten Metals, Slags and Glasses-Characterisation of Properties and Phenomena” held in London in August 2000. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

Development of physicochemical foundations for the synthesis of tungsten-based nanopowders with controlled properties

A chemical and metallurgical method for the preparation of alloyed tungsten-based nanopowders has been developed. The synthesis conditions providing the formation of tungsten-based nanopowders with a specified complex of properties are determined. The chemical and phase compositions and the sizes of nanoparticles and agglomerates of the alloyed tungsten-based nanopowders are studied.     

Thromboxane stimulation of mesangial cell fibronectin synthesis is signalled by protein kinase C and modulated by cGMP

Thromboxane (TX) has been implicated in the pathogenesis of glomerulosclerosis in several models of glomerular injury. In the present study, we examined the role of the protein kinase C (PKC) signalling system in expression of the action of the TXA2/PGH2 analogue U-46619 to stimulate fibronectin (Fn) synthesis in cultured rat mesangial cells (MC), and the influence of cGMP on this MC response. U-46619 activated PKC and enhanced Fn synthesis in MC in a time and concentration dependent fashion. Both responses to U-46619 were blocked by GF 109203X, a selective inhibitor of PKC activity, as well as by calphostin C and staurosporine, PKC inhibitors structurally distinct from GFX. Down-regulation of PKC by prior sustained exposure of MC to 0.5 microM phorbol myristate acetate similarly blocked increases in Fn synthesis induced by U-46619. The TXA2/PGH2 receptor antagonist Sq-29548 also prevented activation of PKC and stimulation of Fn synthesis by U-46619, consistent with transduction of these responses via specific high affinity TXA2/PGH2 receptors on MC. Addition of exogenous 8-Br-cGMP or stimulation of endogenous cGMP generation with atrial natriuretic peptide (ANP) suppressed both U-46619 activation of PKC and stimulation of Fn synthesis. cGMP did not alter TXA2/PGH2 receptor number of affinity in MC, but significantly suppressed phorbol ester activation of PKC. Thus, cGMP inhibition of U-46619 actions is expressed at steps distal to TX receptor binding and may involve effects at and proximal to activation of PKC. Interactions between the PKC and cGMP cellular signalling systems may be important determinants of MC matrix protein production in response to TX.     

Solution and solid phase combinatorial synthesis of peptidomimetic library containing diversified alpha-methylated amino acids

A combinatorial peptidomimetic library containing diversified alpha-methylated amino acids was generated by the Ugi four component condensation (4cc) reaction from acids, amines, isocyanides and ketones in both solution and solid phase synthetic procedures. This one-pot methodology overall gave fair to good yields, which compare well with multi-step syntheses.     

Reversed-phase high-performance liquid chromatographic identification of lutein and zeaxanthin stereoisomers in bovine retina using a C30 bonded phase

There is a considerable degree of variation in the amount of potentiation induced in different animals following the induction of long-term potentiation (LTP). This variation provided us with the opportunity to determine what types of synaptic changes were dependent upon the degree of induced potentiation. To examine possible 'degree of potentiation' effects on synapses, we conducted a multiple regression analysis examining the relationship between the degree of potentiation in LTP animals and a series of synaptic structural measures. We examined synapses in the middle third of the molecular layer (MML) of the rat dentate gyrus following repeated high frequency tetanization of the perforant path. LTP was induced over a 4 h period, and the animals were sacrificed 24 h after the final stimulation. Synapses from the ipsilateral inner third of the dentate molecular layer (IML) and from implanted only animals were also examined for comparison. Ultrastructural quantification included the total number of synapses per neuron, synaptic curvature, the presence of synaptic perforations, and the maximum length of the synaptic apposition. The only structural change that was significantly associated with the degree of potentiation was a positive correlation between the degree of LTP and the number of synapses per neuron. Therefore, synaptic number, while not appearing to be significantly associated with the induction of LTP, appears to be important for the degree of LTP expressed.     

Isolation and biological properties of osteopontin from bovine milk

The right gastroepiploic artery has been increasingly used as a coronary bypass graft. Short- and mid-term patency rates support the supposition that the right gastroepiploic artery is a satisfactory bypass conduit. However, conclusive angiographic data on long-term patency rates are still lacking. An echo-colour Doppler method was used to detect patency of the right gastroepiploic artery grafts through an upper abdominal approach. A group of 24 patients with a right gastroepiploic artery graft to the right or posterior descending coronary artery, all of whom also had a postoperative angiographic study which showed 100% patency of the graft were used as a reference group. A second group of 89 patients was also investigated only with echo-colour Doppler during the postoperative period (mean 8.0 (range 1-48) months). A patent right gastroepiploic artery graft showed a biphasic velocity pattern. Systolic peak velocity ranged from 8 to 26 cm and diastolic peak velocity from 4 to 13 cm. The right gastroepiploic artery diameter ranged from 1.7 to 2.4 mm and flow from 10.2 to 58.8 ml. Among the second group were three patients who had, at their echo-colour Doppler examination, a possible occlusion of the right gastroepiploic artery graft; an angiographic study was conducted and the graft closure confirmed in all cases. Serial echo-colour Doppler evaluation of the right gastroepiploic artery blood flow pattern and diameter is a non-invasive and safe method to check the patency and flow capacity of the artery graft in follow-up studies.     

Phosphoenolpyruvate carboxykinase from Trypanosoma cruzi. Purification and physicochemical and kinetic properties

Phospho enolpyruvate carboxykinase (PEPCK) has been purified to homogeneity from epimastigotes of the Tul 0 strain of Trypanosoma cruzi. The physicochemical parameters determined allowed the calculation of an average molecular mass of 120 kDa; the subunit molecular mass, about 61 kDa, is in good agreement with the value of 58.6 kDa recently determined from the sequence by Sommer et al. (FEBS Lett. 359 (1994) 125-129). The PEPCK from T. cruzi presented, in addition to its molecular mass, typical properties of other ATP-linked PEPCKs, namely strict specificity for ADP in the carboxylation reaction and lower specificity in the decarboxylation and exchange reactions, and synergistic activation by CdCl2 or MgCl2 when added in addition to MnCl2. The enzyme presented hysteretic behaviour, shown by a lag period in the carboxylation reaction, which was affected by dilution and preincubation. The decarboxylation reaction catalyzed by the T. cruzi PEPCK was not inhibited by excess of ATP-Mn. The apparent Km values for the carboxylation reaction, including the low value for PEP (0.035 mM) are compatible with an important role of PEPCK, as suggested by previous NMR experiments, on the CO2 fixation in vivo which leads to succinate excretion during aerobic fermentation of glucose.     

Plasma synthesis and physicochemical certification of chromium boride

Principles for the industrial plasma synthesis of chromium boride CrB₂ are developed. That entails analysis of the current state of its production and use; determination of the characteristics of the three-jet plasma reactor; simulation of the interaction between the raw-material and plasma fluxes; prediction of the characteristics of its synthesis on the basis of the simulation; selection of the optimal technology; implementation of the production technology; physicochemical certification of the chromium boride; and determination of the economic viability of the production process.     

Proteolytic activation of protein C from bovine plasma

Protein C is a vitamin K dependent protein present in bovine plasma (Stenflo, J. (1976), J. Biol. Chem. 251, 355). It is a glycoprotein (mol wt approximately 62 000) composed of a heavy chain (mol wt 41 000) and a light chain (mol wt 21 000). The heavy chain has an amino-terminal sequence of Asp-Thr-Asn-Gln and contains nearly three-fourths of the carbohydrate. The light chain has an amino-terminal sequence of Ala-Asn-Ser-Phe. Incubation of protein C with either factor X activator from Russell's viper venom or trypsin resulted in the cleavage of an Arg-Ile bond between residues 14 and 15 of the heavy chain. Concomitant with this cleavage was the formation of a serine enzyme which was inhibited by diisopropyl phosphorofluoridate. Liberation of the tetradecapeptide decreased the molecular weight of the heavy chain from about 41 000 to 39 000 and resulted in the formation of a new amino-terminal sequence of Ile-Val-Asp-Gly in the heavy chain. No change in the molecular weight of the light chain was observed during the activation reaction. These results indicate that protein C, like the four vitamin K dependent coagulation proteins, exists in plasma in a precursor form and is converted to a serine protease by hydrolysis of a specific Arg-Ile peptide bond. The biological substrate for the enzymatic form of protein C and the physiological mechanism whereby protein C is converted to a serine enzyme are not known.