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Biomedical subjects

G Böhm

Publications and source records attributed to G Böhm.

At least 55 records · Page 3Linked to original sources
PubMed1995

[Gangliocytic paraganglioma of the duodenum].

A duodenal gangliocytic paraganglioma was found to be the cause of nonspecific abdominal complaints in a 68-year-old man with a known carcinoma of the rectum and the prostate. The duodenal gangliocytic paraganglioma is generally regarded as being benign. In this case it is shown to be an additional tumor in a patient with two pre-existent malignancies.

Aged↗
PubMed1994

The effect of ion pairs on the thermal stability of D-glyceraldehyde 3-phosphate dehydrogenase from the hyperthermophilic bacterium Thermotoga maritima.

D-Glyceraldehyde 3-phosphate dehydrogenase from Thermotoga maritima (TmGAPDH) is intrinsically thermostable, exhibiting a thermal transition beyond 105 degrees C. Neither the amino-acid composition nor homology modelling, based on sequence alignment and known 3-D structures of the enzyme from meso- and thermophiles, provide an explanation of the anomalous stability. Recent X-ray data suggest that an increased number of ion pairs is involved. To prove this hypothesis, a number of charged residues contributing to ion pairs in TmGAPDH, but absent in the moderately thermophilic enzyme were altered. Elimination of peripheral ion pairs (E103-K104, E261-R266) was found to be ineffective. Altering a central charge cluster (R10-D47, E314, D*186) led to a drastic decrease in coenzyme binding. As a consequence, guanidine-dependent deactivation is shifted to significantly lower guanidinium chloride (GdmCl) concentrations without altering the denaturation/dissociation profile of the wild type enzyme. Mutants in the S loop (R195D, R195D-D181K) lead to a biphasic profile in the GdmCl-dependent denaturation transition and significant destabilization; at room temperature no subunit dissociation could be observed.

Amino Acid Sequence↗
PubMed1994

A structure-based model for the halophilic adaptation of dihydrofolate reductase from Halobacterium volcanii.

'Halophilic adaptation' of proteins, i.e. the requirement for high concentrations of monovalent ions for thermodynamic stability of proteins from halophilic organisms, is not fully understood. In this work, an explanation for the halophilic behavior of dihydrofolate reductase (h-DHFR) from Halobacterium volcanii is attempted, based on a model structure derived from comparative modeling to dihydrofolate reductase from Escherichia coli. The model structure of h-DHFR shows an unique asymmetrical charge distribution over the protein surface, with positively charged amino acids centered around the active site and negative charges on the opposite side of the enzyme. This particular charge distribution and the correlated molecular dipole are functionally relevant. The negative charges on the surface form clusters which are shielded at high salt concentrations; at low salt, they repulse each other, thus destabilizing the protein. Results are in accordance with denaturation data and, thus, provide an explanation for the exceptional stability properties of h-DHFR.

Amino Acid Sequence↗
PubMed1994

Relevance of sequence statistics for the properties of extremophilic proteins.

The amino acid composition of proteins from mesophilic and extremophilic organisms is commonly assumed to reflect the mechanisms of molecular adaptation to extremes of physical conditions. In this context, halophilic behaviour has been attributed to significantly increased numbers of aspartic and glutamic acid residues. However, extending the analysis to a statistically relevant set of related proteins, dihydrofolate reductase from Halobacterium volcanii, as an example, shows that the increase in negative charge is found to be less significant than other exchanges of amino acids (e.g., Ala, Asn, Arg, Lys, Phe, Ser). Thus, the high water binding capacity of negatively charged residues cannot be unambiguously correlated with the anomalous stability of halophilic proteins. A similar caveat holds for generalizations regarding the thermal stability of proteins. In this case, D-glyceraldehyde-3-phosphate dehydrogenase from the hyperthermophilic bacterium Thermotoga maritima was compared with a number of mesophilic and moderately thermophilic homologs. Again, 'traffic rules of stabilization', in terms of amino acid changes in going from mesophilic to thermophilic proteins, cannot be given.

Amino Acids↗
PubMed1994

[Rheumatoid arthritis of the craniocervical transition. Detection of inflammatory changes in contrast CT and MRI].

A total of 136 patients with rheumatoid arthritis underwent MRI with sagittal T1-weighted spin echo sequences before and after i.v. administration of Gd-DTPA and with a 15-min delay. In addition, T2-weighted gradient echo sequences were performed. Conventional radiographs, including tomography in sagittal and a.p. planes, were also taken of all patients; 51 were also examined by CT before and after i.v. administration of contrast medium and in addition with a 15-min delayed series. The signal intensities of MRI and the changes in density caused by contrast uptake on CT were examined visually and measured quantitatively. The inflammatory changes were classified in four phases by the MRI and CT findings and histological results. A correlation (p < 0.05) was found with the erythrocyte sedimentation rate. MRI was superior to CT in 10% of cases. A discrete effusion in the anterior junction was missed in 4 cases and a hypervascular pannus formation in 1 case by CT. The CT was superior to the other methods in detecting bony lesions and calcifications in the atlantödental region. The local activity of the inflammatory changes can be graded by classifying them with contrast-enhanced MRI and CT, which yield an exact result for better monitoring during therapy.

Adolescent↗