Biomedical subjects

A Poplawski

Publications and source records attributed to A Poplawski.

At least 19 recordsLinked to original sources

PubMed2006

Radiation exposure and dose evaluation in intraoral dental radiology.

In this study, dose area product measurements have been performed to propose diagnostic reference levels (DRLs) in intraoral dental radiology. Measurements were carried out at 60 X-ray units for all types of intraoral examinations performed in clinical routine. The third quartile values calculated range from 26.2 to 87.0 mGy cm(2). The results showed that there exists a large difference between the patient exposures among different dental facilities. It was also observed that dentists working with faster film type or higher tube voltage are not always associated with lower exposure. The study demonstrated the necessity to have the DRLs laid out as guidelines in dental radiology.

Body Burden↗

PubMed2006

Dose-area product measurements in panoramic dental radiology.

In this study, dose-area product (DAP) measurements in panoramic dental radiology have been performed in Germany. The results obtained in this study were proposed as diagnostic reference levels (DRLs). A representative number of dental panoramic units, both with digital and conventional image receptors, have been chosen. Common statistical parameters such as mean, standard deviation and 3rd quartile have been calculated. For four different standard programmes, 'large adult', 'adult male', 'adult female' and 'child', the proposed DRLs are 101, 87, 84 and 75 mGy cm(2), respectively. No clear tendency to a generalised dose reduction from the transition to digital techniques has been observed. Effective doses have been calculated from E/DAP conversion factors published in literature. Even though these values differ by a factor of approximately 3, upper limits of 15.8-21.2 microSv for the four different exposure settings were derived from the data.

Adult↗

PubMed2006

Radiation exposure to children in intraoral dental radiology.

In this study, dose area product (DAP) measurements have been performed aiming at establishing diagnostic reference levels (DRLs) in paediatric intraoral dental radiology. Measurements were carried out at 52 X-ray units for all types of intraoral examinations performed in clinical routine. Not all X-ray units have pre-set child exposure settings with reduced exposure time or in some cases lower tube voltage. Child examinations are carried out using adult exposure settings at these units, which increases the DAP third quartile values by up to 50%. For example, third quartile values for periapical examination ranges from 14.4 to 40.9 mGy cm(2) for child settings and 20.6 to 48.8 mGy cm(2) when the adult settings are included. The results show that there exists a large difference between the patient exposures among different dental facilities. It was also observed that clinics working with faster film type or higher tube voltage are not always associated with lower exposure.

Body Burden↗

PubMed2001

The zinc finger domain of the archaeal minichromosome maintenance protein is required for helicase activity.

The minichromosome maintenance (MCM) proteins, a family of six conserved polypeptides found in all eukaryotes, are essential for DNA replication. The archaeon Methanobacterium thermoautotrophicum Delta H contains a single homologue of MCM with biochemical properties similar to those of the eukaryotic enzyme. The amino acid sequence of the archaeal protein contains a putative zinc-binding domain of the CX(2)CX(n)CX(2)C (C(4)) type. In this study, the roles of the zinc finger domain in MCM function were examined using recombinant wild-type and mutant proteins expressed and purified from Escherichia coli. The protein with a mutation in the zinc motif forms a dodecameric complex similar to the wild-type enzyme. The mutant enzyme, however, is impaired in DNA-dependent ATPase activity and single-stranded DNA binding, and it does not possess helicase activity. These results illustrate the importance of the zinc-binding domain for archaeal MCM function and suggest a role for zinc binding in the eukaryotic MCM complex as well, since four out of the six eukaryotic MCM proteins contain a similar zinc-binding motif.

Amino Acid Sequence↗

PubMed2000

The ftsZ gene of Haloferax mediterranei: sequence, conserved gene order, and visualization of the FtsZ ring.

We sequenced the ftsZ gene region of the halophilic archaeon Haloferax mediterranei and mapped the transcription start sites for the ftsZ gene. The gene encoded a 363-amino-acid long FtsZ protein with a predicted molecular mass of 38 kDa and an isoelectric point of 4.2. A high level of similarity to the FtsZ protein of Haloferax volcanii was apparent, with 97 and 90% identity at the amino acid and nucleotide levels, respectively. Structural conservation at the protein level was shown by visualization of the FtsZ ring structure in H. mediterranei cells using an antiserum raised against FtsZ of H. volcanii. FtsZ rings were observed in cells in different stages of division, including cells with pleomorphic shapes and cells that appeared to be undergoing asymmetric division. Cells were also observed that displayed constriction-like invaginations in the absence of an FtsZ ring, indicating that morphological data are not sufficient to determine whether pleomorphic Haloferax cells are undergoing cell division. Both the upstream and downstream gene order in the ftsZ region was found to be conserved within the genus Haloferax. Furthermore, the downstream gene order, which includes the secE and nusG genes, is conserved in almost all euryarchaea sequenced to date. The secE and nusG genes are likely to be transcriptionally and translationally coupled in Haloferax, and this co-expression may have been a selective force that has contributed to keeping the gene cluster intact.

Amino Acid Sequence↗

PubMed1997

Cell cycle characteristics of thermophilic archaea.

We have performed a cell cycle analysis of organisms from the Archaea domain. Exponentially growing cells of the thermophilic archaea Sulfolobus solfataricus and Sulfolobus acidocaldarius were analyzed by flow cytometry, and several unusual cell cycle characteristics were found. The cells initiated chromosome replication shortly after cell division such that the proportion of cells with a single chromosome equivalent was low in the population. The postreplication period was found to be long; i.e., there was a considerable time interval from termination of chromosome replication until cell division. A further unusual feature was that cells in stationary phase contained two genome equivalents, showing that they entered the resting stage during the postreplication period. Also, a reduction in cellular light scatter was observed during entry into stationary phase, which appeared to reflect changes not only in cell size but also in morphology and/or composition. Finally, the in vivo organization of the chromosome DNA appeared to be different from that of eubacteria, as revealed by variation in the relative binding efficiency of different DNA stains.

Cell Cycle↗

PubMed1977