Selenoprotein gene expression during selenium-repletion of selenium-deficient rats

Selenium repletion of selenium-deficient rats with 20 μg selenium/kg body weight as Na₂SeO₃ was used as a model to investigate the mechanisms that control the distribution of the trace element to specific selenoproteins in liver and thyroid. Cytosolic glutathione peroxidase (cGSHPx), phospholipid hydroperoxide glutathione peroxidase (PHGSHPx), and iodothyronine 5′-deiodinase (IDI) activities were all transiently increased in liver 16 to 32 h after ip injection with selenium. However, only cGSHPx and PHGSHPx activities increased in the thyroid where IDI activity was already increased by selenium deficiency. These responses were owing to synthesis of the seleoproteins on newly synthesised and/or existing mRNAs. The selenoprotein mRNAs in the thyroid gland were increased two- and threefold after the transitory increases in selenoprotein activity. In contrast, there were parallel changes in selenoprotein mRNAs and enzyme activities in the liver, with no prolonged rises in mRNA levels. The organ differences suggest that increased thryotrophin (TSH) concentrations, which are known to induce thyrodial IDI and mRNA, may control the mRNAs for all the thyroidal selenoproteins investigated and be a major mechanism for the preservation of thyroidal selenoproteins when selenium supplies are limited.     

Resistance of spores of some thermophilic actinomycetes to high temperature

Summary The spores of thermophilic actinomycetes were found to be resistant to high temperatures. Spores were more resistant to dry heat than were spores in sucrose solution. The maximum resistance to 100° C in sucrose solution varied from 10 minutes forPseudonocardia thermophila to 4 hours forThermoactinomyces vulgaris.Pseudonocardia thermophila was the most sensitive to dry heat, surviving one-half hour exposure to 100° C, and 3&frac; hours to 90° C. All of the others survived 6 hours of 100° dry heat, exceptThermoactinomyces vulgaris andT. glaucus, both of which survived 15 hours. The other thermophiles tested wereStreptomyces rectus, S. thermoviolaceus subsp.pingens, S. thermovulgaris, andThermomonospora curvata.Contribution No. 342 from the Department of Botany.