Biomedical subjects

C Hammann

Publications and source records attributed to C Hammann.

7 recordsLinked to original sources

PubMed1997

A spermidine-induced conformational change of long-armed hammerhead ribozymes: ionic requirements for fast cleavage kinetics.

The catalytic activity of the trans cleaving hammerhead ribozyme 2as-Rz12, with long antisense flanks of 128 and 278 nt, was tested under a wide range of different reaction conditions for in vitro cleavage of a 422 nt RNA transcript derived from human immunodeficiency virus type 1 (HIV-1). Depending on the reaction conditions, in vitro cleavage rates varied by a factor of approximately 100. Increasing concentrations of magnesium up to 1 M were found to enhance the reaction. Sodium when added simultaneously with magnesium showed an inhibitory effect on the cleavage reaction. Addition of sodium during pre-annealing, however, produced a stimulating effect. It was found that the additional inclusion of spermidine during pre-annealing further increased the reaction rate markedly. In accordance with accelerated cleavage, it was possible to identify a distinct, spermidine-induced conformer of the ribozyme-substrate complex. Under the most favourable conditions cleavage rates of 1/min were obtained, which are in the range of rates obtained for conventional hammerhead ribozymes with short antisense flanks. A comparison of thermodynamic data for short- and long-armed hammerhead ribozymes suggested that the activation entropy became unfavourable when helices I and III formed a long chain ribozyme-substrate complex. We conclude that in the absence of spermidine folding into the active conformation is impaired by increased friction of long helices, resulting in relatively low cleavage rates in vitro.

Catalysis↗

PubMed1997

Crystal structures of modified apo-His117Gly and apo-His46Gly mutants of Pseudomonas aeruginosa azurin.

The X-ray crystal structures of two metal ligand mutants of azurin from Pseudomonas aeruginosa have been solved. In both mutants (His117Gly and His46Gly azurin) one of the copper coordinating histidine residues is replaced by a glycine, creating an empty space in the coordination sphere of the copper ion. The crystal structure of His117Gly azurin at 2.4 A resolution showed that this mutant had undergone partial oxidation at the disulfide bridge between Cys3 and Cys26 and full oxidation at the copper ligand Cys112. There is no copper present in the crystallized form and the bulky group of the oxidized cysteine at position 112 causes large structural rearrangements in the protein structure, especially in the loops connecting the beta-sheets. In the structure of the wild-type holo-azurin from P. aeruginosa the hydrophobic patch is important for the packing of the azurin molecules into dimers which then arrange into tetramers. The completely different packing of the apo-His117Gly mutant can be explained by the disruption of the hydrophobic patch area by the mutation-induced main-chain conformational change of residues 112 to 115. The structure of apo-His46Gly azurin at 2.5 A resolution is the same as the wild-type structure except for the immediate environment at the site of the mutation. In the His46Gly structure water molecules are found at positions that in the wild-type structure are occupied by the imidazole ring of His46 and the copper ion. The imidazole ring of His117 is shifted by about 1 A towards the surface of the protein, similar to that observed for 50% of the molecules in the wild-type apo-azurin structure. This shift causes a slight rearrangement of the monomers within the tetramer such that one local dyad becomes a crystallographic dyad parallel to the c-axis. This leads to a change in the space group from P2(1)2(1)2(1) to P2(1)2(1)2.

Azurin↗

PubMed1996

X-ray crystal structure of the two site-specific mutants Ile7Ser and Phe110Ser of azurin from Pseudomonas aeruginosa.

The blue copper protein azurin from Pseudomonas aeruginosa contains a single Trp residue that is believed to be involved in the inducible intramolecular electron transfer from a disulphide group to the copper centre. This residue shows in fluorescence spectra the highest energy emission of tryptophan-containing compounds at room temperature, which is explained by its rigid and highly hydrophobic environment. In order to investigate the role of the Trp residue in electron transfer and the influence of its environment, two mutations (17S and F110S) were introduced that were thought to increase the polarity and the mobility in its environment. The crystal structures of these mutants were solved at 2.2 A and 2.3 A resolution, respectively. These provide a structural basis for the changes observed in fluorescence spectra compared with the wild-type protein. We conclude from our results that these changes are not caused by a change in the dynamics of the Trp residue itself, but exclusively by an increased effective dielectric constant of the microenvironment of Trp48 and by changes in mobility of the mutated residues.

Azurin↗

PubMed1996

Comparison of effects of topical levocabastine and nedocromil sodium on the early response in a conjunctival provocation test with allergen.

BACKGROUND: Multiple ocular challenges or seasonal trials have demonstrated the efficacy of levocabastine and nedocromil sodium in the treatment of allergic conjunctivitis. OBJECTIVE: This study was designed to compare the protective effect of levocabastine eye drops with that of nedocromil in a conjunctival provocation test with allergen. METHODS: Twenty-four patients with allergic conjunctivitis to grass pollen were recruited. After a preliminary provocation to determine conjunctival reaction threshold (erythema of at least 50% of the conjunctiva with ocular itching), patients were randomized to receive either topical levocabastine (0.05%) or nedocromil (2%) 15 minutes before provocation. Erythema and pruritus intensity were recorded at each concentration of allergen up to the reaction threshold. RESULTS: The allergen concentration level necessary to reach reaction threshold was increased (p < 0.001) after treatment with both drugs. Comparison between screening and each treatment indicated that the shift in allergen concentration was significantly greater after levocabastine treatment than after nedocromil treatment (p = 0.019). Conjunctival itching (symptom score) and erythema (percent conjunctival surface) were also better controlled by levocabastine than by nedocromil during provocation (p < 0.05). CONCLUSION: In a provocation test with allergen, levocabastine and nedocromil were both effective in increasing the conjunctival tolerance to allergen, with better protection provided by levocabastine.

Administration, Topical↗

PubMed1995

[Horton's disease: ophthalmological and neurological complication].

We report the case of a 74-year-old women admitted to the hospital because of rapidly developing diplopia. The admission anamnesis revealed fronto-temporal headaches and pain in the maxilla for three days. A cerebral cT scan was normal, and a corticosteroid therapy was initiated. Diagnosis of Horton's syndrome was confirmed by the good response to treatment and by biopsy of the temporal artery. Different ocular and neurologic complications of Horton's disease, their clinical appearances and therapeutic measures are discussed by the authors.

Acute Disease↗

PubMed1995

[Anaphylactic shock].

Anaphylactic shock is an unexpected, sudden and sometimes deadly event that attacks the patient in 75% of the cases without pre-existent history of allergy. In general, drugs, hymenopteric poisons and nutrients (according to the recent concept) are responsible. Beside the classical IgE-mediated anaphylactic shock there exists another anaphylactic shock, identical in its clinical picture and treatment but not in the mechanism of development. Epinephrine is the only effective drug in case of respiratory (bronchial asthma, laryngeal edema) or cardiovascular (hypotension, arrhythmias, hypovolemic shock) manifestation. It has to be administered as rapidly as possible.

Anaphylaxis↗

PubMed1993

[Drug-induced calculi].

Drug-induced urinary calculi are rarely observed. However, it is useful to know this etiology. A complete anamnesis of drugs and dosages is mandatory if a patient presents with lithiasis, since some pharmacotherapies may carry an enhanced lithogenic risk. The list of lithogenic drugs is discussed. In order to yield preventive data, infrared, spectrophotometry is the best available analytic method.

Allopurinol↗