When hemolyzates from erythrocytes of selenium-deficient rats were incubated in vitro in the presence of ascorbate or H(2)O(2), added glutathione failed to protect the hemoglobin from oxidative damage. This occurred because the erythrocytes were practically devoid of glutathione-peroxidase activity. Extensively purified preparations of glutathione peroxidase contained a large part of the (75)Se of erythrocytes labeled in vivo. Many of the nutritional effects of selenium can be explained by its role in glutathione peroxidase.

No abstract

No abstract

These experiments compared the metabolism of the N-acetylated derivatives of D- or L-methionine to that of L-methionine. Spargue-Dawley rats were orally or intraperitoneally dosed with N-[1-14C]acetyl-L-methionine, N-[1-14C]acetyl-D-methionine, or sodium [1-14C]acetate. 14CO2 was collected at intervals over 24 hours. In addition, groups of rats were orally dosed with either 35S-labeled N-acetyl-L-methionine or L-methionine. The animals were killed 3, 24, and 168 hours after dosing. Urine and feces were collected, and tissues were excised for 35S determinations. With either route of dosing, N-[1-14C]acetyl-L-methionine yielded the same amount of 14CO2 as sodium [1-14C]acetate over a 24-hour period. The acetate moiety of N-[1-14C]acetyl-D-methionine is not readily metabolized to 14CO2. Within each time period after dosing, the tissue distribution of 35S from 35S-labeled N-acetyl-L-methionine and L-methionine was similar. Protein specific activities for the two isotopes were also the same. After 168 hours, 30% of both isotopes of 35S appeared in the urine and feces, and the two isotopes were similarly distributed in the organic -S and inorganic -S fractions of urine. The studies show that L-methionine from N-acetyl-L-methionine is metabolically equivalent to free L-methionine. This conclusion is consistent with rat feeding studies showing that N-acetyl-L-methionine is nutritionally equivalent to L-methionine.

No abstract