ABSTRACT
The iron of the binuclear active center of [NiFe]-hydrogenases carries two CN and one CO ligands which are thought to confer to the metal a low oxidation and/or spin state essential for activity. Based on the observation that one of the seven auxiliary proteins required for the synthesis and insertion of the [NiFe] cluster contains a sequence motif characteristic of O-carbamoyl-transferases it was discovered that carbamoyl phosphate is essential for formation of active [NiFe]-hydrogenases in vivo and is specifically required for metal center synthesis suggesting that it is the source of the CO and CN ligands. A chemical path for conversion of a carbamoyl group into cyano and carbonyl moieties is postulated
Subject(s)
Carbamyl Phosphate/metabolism , Escherichia coli/enzymology , Hydrogenase/biosynthesis , Hydrogenase/chemistry , Iron/metabolism , Amino Acid Motifs , Binding Sites , Cell Extracts , Escherichia coli/metabolism , Hydrogenase/metabolism , Ligands , Models, Biological , Protein SubunitsABSTRACT
A fiber optic biosensor for the detection of fibrinolytic products produced during lysis of "soft" blood clots is described. The biosensor was constructed to be selective toward D dimer antigens, which form from the dissolution of cross-linked fibrin clots. The presence of D dimer antigens above a threshold level is a clinical diagnostic used to determine the presence of such occlusions following a stroke. Fluorescein-labeled D dimer antibodies are immobilized on the tip of an optical fiber by dip coating from a silica sol-gel solution. When D dimer antigens combine with the antibodies, fluorescence intensity decreases. The response of the sensor was examined in phosphate buffered saline, human plasma, and blood. Calibration plots for the sensor were obtained in the clinically significant D dimer concentration range from 0.54 microgram/ml to 6 micrograms/ml. Changes in spectroscopic properties as the sol-gel encapsulated tagged antibodies aged were examined; a decrease in fluorescence intensity with age was noted. The D dimer antibodies remain viable for at least 4 weeks while encapsulated in the sol-gel network when stored at 4 degrees C in PBS solution. This novel sensor is being developed for use with other catheter-based microtools to treat stroke resulting from occlusion in the vascular system.
Subject(s)
Antigen-Antibody Reactions , Biosensing Techniques/instrumentation , Fiber Optic Technology , Silicone Gels , Animals , Calibration , Drug Monitoring/methods , Feasibility Studies , Fibrin Fibrinogen Degradation Products/analysis , Fibrinolytic Agents/blood , Fibrinolytic Agents/therapeutic use , Fluorescein/analysis , Humans , Kinetics , Mice , Optical Fibers , Sensitivity and Specificity , Stroke/blood , Stroke/drug therapyABSTRACT
1. Biological and biomimetic oxidations of thioethers are reviewed. 2. gamma-Radiolysis, pulse radiolysis, photochemical, chemical, and electrochemical methods for generating sulphur cation radicals are discussed and exemplified. 3. The major reactions of sulphur cation radicals: nucleophilic attack, electron transfer, decarboxylation, reaction with O2, C-S, C-C, and alpha-C-M bond cleavages, sulphur abstraction, and rearrangements are presented.
Subject(s)
Free Radicals/metabolism , Sulfur/metabolism , Animals , Cations/chemistry , Cations/metabolism , Cations/radiation effects , Free Radicals/chemistry , Free Radicals/radiation effects , Humans , Sulfur/chemistry , Sulfur/radiation effectsSubject(s)
Drosophila Proteins , Organophosphorus Compounds/chemical synthesis , Organoselenium Compounds/chemical synthesis , Phosphates/chemical synthesis , Phosphates/metabolism , Phosphotransferases , Selenium Compounds/chemical synthesis , Selenium Compounds/metabolism , Anaerobiosis , Bacterial Proteins/metabolism , Escherichia coli/enzymology , Escherichia coli/genetics , Hydrolysis , Recombinant Proteins/metabolism , Reference Standards , Selenium RadioisotopesABSTRACT
Anodic oxidation of methionine under different pH conditions is reported. The results are compared with the oxidation process when the glycinic terminus of methionine is coordinated with Co(III). Synthesis of [Co(en)2(L-Met)](ClO4)2, [Co(trien)(L-Met)](CF3SO3)2, and [Co(trien)(OSO2CF3)2]CF3SO3 is reported where L-methionine, en = ethylenediamine, trien = triethylenetetraamine. The triflato complex ([Co(trien)(OSO2CF3)2]CF3SO3) can serve as a starting material for synthesizing a variety of complexes. The x-ray structure of [Co(en)2(L-Met)](CIO4)2.H2O is also presented The complex crystallizes in space group P21 of the monoclinic system with two independent molecules in the crystallographic asymmetric unit. The unit cell dimensions are a = 9.582 (2) A, b = 11.554 (2) A, c = 19.988 (6) A, and beta = 98.85 (2) degrees. The two molecular units are related by a pseudo-center of symmetry. The electrochemical data presented here suggest a major role of the neighboring group and pH in defining the ease of oxidation of methionine.
Subject(s)
Crystallography, X-Ray , Methionine/chemistry , Organometallic Compounds/chemistry , Cobalt/chemistry , Electrochemistry , Hydrogen-Ion Concentration , Models, Molecular , Molecular Structure , Oxidation-ReductionABSTRACT
A labile, selenium donor compound required for synthesis of selenium-dependent enzymes and seleno-tRNAs is formed from ATP and selenide by the SELD enzyme. This compound, tentatively identified as a selenophosphate [Veres, Z., Tsai, L., Scholz, T. D., Politino, M., Balaban, R. S., & Stadtman, T. C. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 2975-2979], is indistinguishable from chemically prepared monoselenophosphate by 31P NMR spectroscopy and ion pairing HPLC. Furthermore, addition of chemically prepared monoselenophosphate caused a dose-dependent decrease in the amount of 75Se incorporated into tRNAs from 75SePX generated in situ by SELD enzyme. A procedure is described for the chemical synthesis of monoselenophosphate in which the readily prepared (MeO)3PSe is converted in quantitative yield to (TMSO)3PSe followed by complete cleavage of the latter to monoselenophosphate in oxygen-free aqueous buffer. The chemical properties of chemically synthesized monoselenophosphate are described.
Subject(s)
Drosophila Proteins , Phosphates/chemistry , Phosphates/metabolism , Phosphotransferases , Selenium Compounds/chemistry , Selenium Compounds/metabolism , Adenosine Triphosphate/metabolism , Bacterial Proteins/metabolism , Magnetic Resonance Spectroscopy , RNA, Transfer/metabolism , Salmonella/enzymologyABSTRACT
Metal-backed acetabular components offer the advantage of a lower incidence of loosening. The case of a 33-year-old man emphasizes the potential problem of fracture of both the polyethylene and metal-backed structures. Although this case report may represent an unusual and infrequent occurrence, it emphasizes a potential failure mode for acetabular components with metal backing. While fracture of the polyethylene has been previously reported, little thought has been given to the further potential of fracture of metal-backed support. The clinical profile as well as the roentgenographic appearance of such a phenomenon is presented for further sophistication of the surgeon when dealing in the challenging area of hip arthroplasty.
Subject(s)
Acetabulum/diagnostic imaging , Fractures, Bone/etiology , Hip Prosthesis , Adult , Fractures, Bone/diagnostic imaging , Humans , Male , Prosthesis Failure , Radiography , ReoperationABSTRACT
Seven cases of ossicles in the posterior horn of the medial meniscus revealed that: trauma is not necessarily an antecedent; some knees with ossicles are asymptomatic; some knees may be treated conservatively and without surgery; ossicles can be distinguished from loose bodies under fluoroscopic examination. Microscopically the ossicles are living bone. Although the etiology is not proven, perhaps merit should be given to the theory of a vestigial or sesamoid-like bone.
