A new proposal for urease mechanism based on the crystal structures of the native and inhibited enzyme from Bacillus pasteurii: why urea hydrolysis costs two nickels.

BACKGROUND: Urease catalyzes the hydrolysis of urea, the final step of organic nitrogen mineralization, using a bimetallic nickel centre. The role of the active site metal ions and amino acid residues has not been elucidated to date. Many pathologies are associated with the activity of ureolytic bacteria, and the efficiency of soil nitrogen fertilization with urea is severely decreased by urease activity. Therefore, the development of urease inhibitors would lead to a reduction of environmental pollution, to enhanced efficiency of nitrogen uptake by plants, and to improved therapeutic strategies for treatment of infections due to ureolytic bacteria. Structure-based design of urease inhibitors would require knowledge of the enzyme mechanism at the molecular level. RESULTS: The structures of native and inhibited urease from Bacillus pasteurii have been determined at a resolution of 2.0 A by synchrotron X-ray cryogenic crystallography. In the native enzyme, the coordination sphere of each of the two nickel ions is completed by a water molecule and a bridging hydroxide. A fourth water molecule completes a tetrahedral cluster of solvent molecules. The enzyme crystallized in the presence of phenylphosphorodiamidate contains the tetrahedral transition-state analogue diamidophosphoric acid, bound to the two nickel ions in an unprecedented mode. Comparison of the native and inhibited structures reveals two distinct conformations of the flap lining the active-site cavity. CONCLUSIONS: The mode of binding of the inhibitor, and a comparison between the native and inhibited urease structures, indicate a novel mechanism for enzymatic urea hydrolysis which reconciles the available structural and biochemical data.

Cytokine gene expression and production by human LPS-stimulated mononuclear cells are inhibited by sulfated heparin-like semi-synthetic derivatives.

BACKGROUND: The K5 polysaccharide obtained from Escherichia coli strain 010:K5:H4 is a polymer of the disaccharidic unit formed by D-glucuronic acid and N-acetylglucosamine. This structure is akin to N-acetylheparosan, the precursory polymer of heparin and of heparan sulfate. This structural affinity with N-acetylated heparin and with de-sulfated heparin makes the K5 polysaccharide extremely useful for the preparation of sulfated heparin-like semi-synthetic derivatives. It has been demonstrated that heparins are able to inhibit tissue factor and cytokine production and expression by human monocytes. OBJECTIVE: The aim of this study was to evaluate the effects of four different heparin-like semi-synthetic derivatives on inflammatory cytokine production and expression by human mononuclear cells. RESULTS: The simultaneous addition of lipopolysaccharide (LPS; 0.2 and 10 micro g mL(-1)) and the K5 polysaccharide did not inhibit interleukin (IL)-1beta, IL-6 or tumor necrosis factor (TNF)-alpha production by stimulated mononuclear cells. IL-1beta, IL-6 and TNF-alpha concentrations in supernatants of LPS-stimulated mononuclear cells were not influenced by the addition of N,O-sulfated K5 polysaccharide (K5-N, OS) and epimerized N-sulfated K5 polysaccharide (K5 NS epi) at 5 and 10 microg mL(-1), whereas the addition of epimerized N,O-sulfated K5 polysaccharide (K5-N, OS epi) (5 and 10 microg mL(-1)) and O-sulfated K5 polysaccharide (K5-OS) (5 and 10 microg mL(-1)) to LPS-stimulated cells caused a significant dose-dependent inhibition of IL-1beta, IL-6 and TNF-alpha. All sulfated heparin-like semi-synthetic derivatives did not influence the IL-10 production by LPS-stimulated mononuclear cells. In LPS-stimulated cells (0.2 and 10 microg mL(-1)), K5-OS or K5-N, OS epi at 5 and 10 microg mL(-1) markedly decreased TNF-alpha mRNA expression. CONCLUSIONS: These results indicate that the sulfated heparin-like semi-synthetic derivatives K5-OS and K5-N, OS epi are able to inhibit both expression and production of inflammatory cytokines, whereas they do not influence the anti-inflammatory cytokine IL-10, suggesting a potential role for these products as modulators of inflammatory reactions.

[The effect of various drugs on post-operative pain-producing sensations]. / Influenza di alcune sostanze farmacologiche nella sensazione algogena postoperatoria.

The influence of diazepam, the hemisuccinic ester of oxazepam, fentanyl and pentazocine on pain-producing sensation after surgery was tested in 160 patients subjected to ordinary and major surgery. Use was made of Dundee and Moore's modification of Clutton-Brock's test, and Bromage's test. Analysis of the results indicated that the slow administration of analgesics and psychoactive drugs enables better results to be achieved, with smaller amounts of active substance.

[Glucagon and renal function in arterial hypotension (experimental study)]. / Glucagone e funzione renale in corso di ipotensione arteriosa (Indagine sperimentale).

The effects of glucagon on the renal function of dogs in posthaemorrhagic hypotension has been investigated. A significant improvement in renal emunctory function was noted after administration (with physiological solution vehicle) of glucagon under these conditions. Following these encouraging results, findings have been transferred to clinical practice.

The complex of Bacillus pasteurii urease with acetohydroxamate anion from X-ray data at 1.55 A resolution.

The structure of Bacillus pasteurii urease inhibited with acetohydroxamic acid was solved and refined anisotropically using synchrotron X-ray cryogenic diffraction data (1.55 A resolution, 99.5% completeness, data redundancy = 26, R-factor = 15.1%, PDB code 4UBP). The two Ni ions in the active site are separated by a distance of 3.53 A. The structure clearly shows the binding mode of the inhibitor anion, symmetrically bridging the two Ni ions in the active site through the hydroxamate oxygen and chelating one Ni ion through the carbonyl oxygen. The flexible flap flanking the active site cavity is in the open conformation. The possible implications of the results on structure-based molecular design of new urease inhibitors are discussed.

[Epilepsy following cisternography with water-soluble contrast (author's transl)]. / Epilessia da cisternografia con contrasto idrosolubile triodato.

A case of epilepsy is reported during ventriculography with hydrosoluble triiodate contrast (methylglutamine iotalamate). The cysternal interhemispheric cavities of the midline were flooded. This complication, which could have been lethal was treated with thiopental sodium salt, 6 methylprednisolone, mannitol, curare, trans-larynx intubation, ventilation with oxygen and nitrous oxide. The AA. conclude that the presence of an anaesthetist-resuscitator is essential during ventriculography with triiodate hydrosoluble contrast medium.