beta rays
Dotaz
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2. izd 207 s. : obr., tab.
- MeSH
- beta částice MeSH
- radioaktivita MeSH
- záření MeSH
- Publikační typ
- monografie MeSH
- Konspekt
- Přírodní vědy. Matematické vědy
- NLK Obory
- přírodní vědy
The determination of the presence of artificial radionuclides in the air is mainly accomplished by using gamma spectrometry analysis of filter samples. This work suggests very fast, reliable and efficient methods for tentative quantitative determination of the activity of artificial nuclides such as transuranic elements, strontium, yttrium, etc. in the air based only on the gross alpha and beta volume activity. The main aspect of these methods is to provide information about approximate results for the gross alpha and beta activity of air filters, thus it is convenient as a triage technique. Unlike gamma spectrometry, the methods are not qualitative but it allows the preliminary estimation of the presence of non-natural radionuclides. The influence of increment of the dust layer on self-absorption of alpha/beta particles was also studied. The methods are particularly suitable for screening situations where radionuclide identification is not necessary.
The X-ray structure of cold-active beta-galactosidase (isoenzyme C-2-2-1) from an Antarctic bacterium Arthrobacter sp. C2-2 was solved at 1.9A resolution. The enzyme forms 660 kDa hexamers with active sites opened to the central cavity of the hexamer and connected by eight channels with exterior solvent. To our best knowledge, this is the first cold-active beta-galactosidase with known structure and also the first known beta-galactosidase structure in the form of compact hexamers. The hexamer organization regulates access of substrates and ligands to six active sites and this unique packing, present also in solution, raises questions about its purpose and function. This enzyme belongs to glycosyl hydrolase family 2, similarly to Escherichia coli beta-galactosidase, forming tetramers necessary for its enzymatic function. However, we discovered significant differences between these two enzymes affecting the ability of tetramer/hexamer formation and complementation of the active site. This structure reveals new insights into the cold-adaptation mechanisms of enzymatic pathways of extremophiles.
- MeSH
- Arthrobacter enzymologie MeSH
- bakteriální proteiny genetika chemie metabolismus MeSH
- beta-galaktosidasa genetika chemie metabolismus MeSH
- financování organizované MeSH
- ionty chemie MeSH
- krystalografie rentgenová MeSH
- kvarterní struktura proteinů MeSH
- lidé MeSH
- molekulární modely MeSH
- molekulární sekvence - údaje MeSH
- nízká teplota MeSH
- rozpouštědla chemie MeSH
- sekvence aminokyselin MeSH
- sekvenční seřazení MeSH
- vazebná místa MeSH
- Check Tag
- lidé MeSH
