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Biomedical subjects

H Berk

Publications and source records attributed to H Berk.

At least 19 recordsLinked to original sources
PubMed2004

Tuberculous meningitis in adults--experience from Turkey.

BACKGROUND: The annual incidence of tuberculous meningitis (TM) is unknown. TM is a disease that still often results in residual sequelae, and has a mortality rate ranging between 15 and 51%. Experience of countries such as Turkey where drug-resistant tuberculosis and TM are prevalent is important. METHODS: Clinical and laboratory findings of 42 patients with TM, followed between 1991 and 2002, were evaluated retrospectively. RESULTS: Twenty-eight female and 14 male patients were included in this study. The mean age of the patients was 33.9 +/- 13.2 years (range, 16-60 years). Fourteen had a history of pulmonary tuberculosis; 12 reported close contact with a person with active pulmonary tuberculosis; three were diagnosed with active pulmonary tuberculosis; two, with HIV infection; two, with Pott's disease; and one, with systemic lupus erythematosus. On admission, 17 patients were diagnosed with stage I; 15, with stage II; and 10, with stage III disease. Hemiparesis (35.7%), cranial nerve palsy (30.9%), and altered consciousness (26.9%) were the most common neurological deficits. Prolonged duration of pre-existing symptoms and female gender were found as significant risk factors in those who develop neurological sequelae (p < 0.01 and p < 0.05, respectively). Cranial computerised tomography revealed various pathological findings in all but five patients. Sulcus effacement was the most common radiological finding. Enlargement of ventricles, focal cerebral oedema/shunt, calcification of meninges, tubercle, and infarction were other common abnormal radiological findings. CONCLUSIONS: Prolonged duration of pre-existing symptoms and female gender are predictors of neurological sequelae of TM. Early identification of such patients and prompt initiation of anti-tuberculosis therapy may improve their outcome.

Adolescent↗
PubMed2002

Biocompatibility tests on the intraocular vision aid IOVA.

Intraocular miniaturized image transmission systems are developed to restore vision in patients with irreversible destruction of the anterior ocular segment (i.e. chemical burns, explosion trauma, trachoma) and high risk for corneal transplantation, provided that the posterior ocular segment is intact. To ensure safety of such a device biocompatibility tests were conducted. In the present study the effects of light and temperature in various intensities and the toxicity of the implanted materials on neural function in the rabbit retina in-vivo was investigated. All tests give encouraging results concerning the feasibility of intraocular miniaturized image transmission systems.

Animals↗
PubMed1999

Successful long-term implantation of electrically inactive epiretinal microelectrode arrays in rabbits.

BACKGROUND: In the ongoing discussion concerning the realization of an epiretinal prosthesis for electric stimulation of retinal ganglion cells, long-term fixation of such a device is a crucial question. We evaluated surgical techniques for implantation and fixation of electrically inactive microelectrode arrays (MA) into the retinas of rabbits and secondary tissue reactions to the implant. METHODS: Vitrectomy and laser coagulation of the prospective fixation area were performed in rabbits. Implantation of MAs was performed 3 weeks later in 10 animals. The MA was fixated using retinal tacks. The follow-up included ophthalmoscopy and electrophysiology. At the end of the follow-up, the enucleated eyes were processed for light microscopy using standard procedures and grinding techniques. RESULTS: Nine of 10 rabbits were implanted without serious complications. Clinical and electrophysiologic data through 6 months of follow-up did not indicate any adverse effect of the surgery, the implant, or the tack itself. No change in retinal architecture underneath the implant was found by light microscopy. In these cases, the implant was stable at its original fixation area. In three cases, mild cataract formation was observed, and in one case, a total retinal detachment was found. CONCLUSION: Tack fixation of electrode arrays for electric stimulation of the inner retinal surface seems to be a useful approach in long-term implantation of an epiretinal prosthesis.

Animals↗
PubMed1998

F420H2:NADP oxidoreductase from Methanobacterium thermoautotrophicum: identification of the encoding gene via functional overexpression in Escherichia coli.

F420H2:NADP oxidoreductase is found in methanogenic, sulfate-reducing and halophilic archaea and also in some bacteria. The putative gene encoding the enzyme was cloned from Methanobacterium thermoautotrophicum (strain Marburg) and heterologously expressed in Escherichia coli. The overproduced active enzyme was purified, characterized and crystallized.

Chromatography↗
PubMed1997

The adenylate kinase genes of M. voltae, M. thermolithotrophicus, M. jannaschii, and M. igneus define a new family of adenylate kinases.

The adenylate kinase genes (adkA) were cloned from four closely related methanogenic members of the Archaea: the mesophile Methanococcus voltae (Mv), the thermophile M. thermolithotrophicus (Mt) and the hyperthermophiles M. jannaschii (Mj) and M. igneus (Mi). All four genes encode a protein of 192 amino acids (aa), and the four enzymes were closely related, with 68-81% aa identity in pairwise comparisons. It is anticipated that the enzyme set will provide the basis for studies that can establish the structural basis for ADK thermal stability. Mj and Mi contained a gene homologous to M. vannielii sec Y upstream of adkA, while Mv and Mt contained an unidentified, yet conserved, upstream open reading frame (ORF). Mt, Mj and Mi, but not Mv, contained an unidentified, yet highly conserved, ORF directly downstream of adkA. Based on their size, predicted secondary structure and phylogenetic relation to bacterial and eukaryotic adenylate kinases (ADK), it was concluded that the archaeal adkA genes encoded a unique class of ADK, and suggested that Euryarchaeotal and Crenarchaeotal branches of the Archaea contain separate subclasses of the enzyme.

Adenylate Kinase↗
PubMed1997

Function of coenzyme F420-dependent NADP reductase in methanogenic archaea containing an NADP-dependent alcohol dehydrogenase.

Methanogenic archaea growing on ethanol or isopropanol as the electron donor for CO2 reduction to CH4 contain either an NADP-dependent or a coenzyme F420-dependent alcohol dehydrogenase. We report here that in both groups of methanogens, the N5, N10-methylenetetrahydromethanopterin dehydrogenase and the N5, N10-methylenetetrahydromethanopterin reductase, two enzymes involved in CO2 reduction to CH4, are specific for F420. This raised the question how F420H2 is regenerated in the methanogens with an NADP-dependent alcohol dehydrogenase. We found that these organisms contain catabolic activities of an enzyme catalyzing the reduction of F420 with NADPH. The F420-dependent NADP reductase from Methanogenium organophilum was purified and characterized. The N-terminal amino acid sequence showed 42% sequence identity to a putative gene product in Methanococcus jannaschii, the total genome of which has recently been sequenced.

Alcohol Oxidoreductases↗
PubMed1996

Re-face stereospecificity at C4 of NAD(P) for alcohol dehydrogenase from Methanogenium organophilum and for (R)-2-hydroxyglutarate dehydrogenase from Acidaminococcus fermentans as determined by 1H-NMR spectroscopy.

The two diastereotopic protons at C4 of NAD(P)H are seen separately in 1H-NMR spectra. This fact was used to determine the stereospecificity at C4 of NAD(P) for the NADP-dependent alcohol dehydrogenase from Methanogenium organophilum and for the NAD-dependent (R)-2-hydroxyglutarate dehydrogenase from Acidaminococcus fermentans. The reduction of NADP+ with [2H6]ethanol was found to yield (4R)-[4-2H1]NADPH and the oxidation of (4R)-[4-2H1]NADH with 2-oxoglutarate to yield unlabelled [4-1H]NAD+. These results indicate that both enzymes are Re-face stereospecific at C4 of the pyridine nucleotides.

Alcohol Dehydrogenase↗
PubMed1996

Si-face stereospecificity at C5 of coenzyme F420 for F420-dependent glucose-6-phosphate dehydrogenase from Mycobacterium smegmatis and F420-dependent alcohol dehydrogenase from Methanoculleus thermophilicus.

Coenzyme F420 is a 5-deazaflavin. Upon reduction, 1,5-dihydro-coenzyme F420 is formed with a prochiral center at C5. In this study we report that the F420-dependent glucose-6-phosphate dehydrogenase from Mycobacterium smegmatis and the F420-dependent alcohol dehydrogenase from Methanoculleus thermophilicus are Si-face stereospecific with respect to C5 of the 5-deazaflavin. These results were obtained by following the stereochemical course of the reversible incorporation of 3H into F420 from tritium-labeled substrates. Our findings bring to eight the number of coenzyme-F420-dependent enzymes shown to be Si-face stereospecific. No F420-dependent enzyme with Re-face stereospecificity is known. This is noteworthy since coenzyme F420 is functionally similar to pyridine nucleotides for which both Si-face and Re-face specific enzymes have been found.

Alcohol Dehydrogenase↗
PubMed1975

Clinical situations in which amputation is preferred to pulp capping because of biologic considerations.

Calcium hydroxide, in its various forms, has become the preferred agent of most practitioners who perform pulp capping. The application of calcium hydroxide to the pulp stimulates the growth of new dentin and protects the pulp from subsequent irritation. However, the new dentin generated by the pulp may, in turn, infringe on the pulp. If the thickness of the pulp tissue is large, this infringement will not be significant. If the volume of pulp tissue is shallow, the same amount of infringement may cause sufficient impairment of circulation to the cornal area of the pulp, leading to an area of the necrosis may then contaminate the entire pulp, and root canal therapy will become necessary. Therefore, pulpal amputation is the preferred treatment in such situations.

Calcium Hydroxide↗