Promotion of lipid oxidation by selenate and selenite and indicators of lipid peroxidation in the rat.

The AIN-93 reformulation of the AIN-76A rodent diet includes a change in selenium supplement from sodium selenite to sodium selenate to reduce dietary lipid peroxidation. A change to selenate as the standard form of Se in rat diets would render results from previous work using selenite less relevant for comparison with studies using the AIN-93 formulation. To critically examine the rationale for the AIN-93 recommendation, we prepared Torula yeast basal diets patterned as closely as possible after the AIN-93 formulation and supplemented with 0, 0.15 (adequate), or 2.0 (high) mg selenium/kg diet as sodium selenite or sodium selenate. Livers isolated from male Sprague-Dawley rats fed these diets for 15 wk showed no differences in thiobarbituric acid-reactive substances or lipid hydroperoxides measured with the ferrous oxidation in xylenol orange method. Lipids isolated from samples of high-selenate and high-selenite diets showed no differences in conjugated dienes. The addition of selenate or selenite to soybean oil did not result in an altered Oil Stability Index. These results demonstrate that selenate is not less likely than selenite to cause oxidation of other dietary components. Benefits of selenate over selenite in the diets of rodents remain to be demonstrated.

Role of the Gp16 lytic transglycosylase motif in bacteriophage T7 virions at the initiation of infection.

The predicted catalytic glutamate residue for transglycosylase activity of bacteriophage T7 gp16 is not essential for phage growth, but is shown to be beneficial during infection of Escherichia coli cells grown to high cell density, conditions in which murein is more highly cross-linked. In the absence of the putative transglycosylase, internalization of the phage genome is significantly delayed during infection. The lytic transglycosylase motif of gp16 is essential for phage growth at temperatures below 20 degrees C, indicating that these growth conditions also lead to increased cross-linking of peptidoglycan. Overexpression of sltY, E. coli soluble lytic transglycosylase, partially complements the defect in infection of mutant phage particles, allowing them to infect at higher efficiencies. Conversely, an sltY deletion increases the latent period of wild-type phage.