Effects of Chemical Form and Dosage on the Incorporation of Selenium into Tissue Proteins in Rats

Abstract

We investigated the incorporation of Se into the proteins of liver and muscle, the two main Se pools, during replenishment of Se-deficient rats with normal or large doses of 75Se-labeled selenite and selenomethionine, doses equivalent to the amounts ingested from a diet with 0.2 or 2 mg Se/kg. With the higher intake, Se levels were elevated. More Se was retained from selenomethionine than from selenite. After separation of the labeled proteins, it was apparent that the higher tissue Se contents were mainly due to nonspecific incorporation into a large number of proteins. We observed no differences between the two chemical forms with regard to the formation of the specific selenoproteins. The 10-fold increase in the Se supply led to a relatively small rise in the levels of these compounds. The results indicate that after ingestion of normal amounts of selenite nearly all of the element is present in the specific selenoproteins. With increasing doses a part is also incorporated nonspecifically into numerous other proteins. In the case of selenomethionine, a part of the element follows the same metabolic pathways, but a percentage is also deposited directly and nonspecifically into proteins in place of methionine.

Plasma selenoprotein P levels of healthy males in different selenium status after oral supplementation with different forms of selenium

“…The subject with initially higher selenium intake would likely reach a higher plasma selenium level after supplementation than the subject with initially low selenium intake. Dietary methionine may also in¯uence the amount of selenium available for synthesis of selenoproteins since it competes with selenomethionine for incorporation into proteins (Luo et al, 1985;Waschulewski & Sunde, 1988;Behne et al, 1991). Since there were no signi®cant differences in selenoprotein P levels between subjects given organic and inorganic forms of selenium in Trial I, the methionine supply of the subjects was probably suf®cient making possible a high utilisation of selenium from the selenomethionine supplement for synthesis of selenoprotein P. The difference between organic and inorganic selenium supplements can also be interpreted from the selenoprotein/ selenium ratios.…”

“…Although regulation at the transcriptional level has been observed for selenoproteins (O'Prey et al, 1993), there is little evidence that selenium supply exerts its in¯uence via such mechanisms (Burk, 1997). The biosynthesis of individual selenoproteins in different selenium states is tissue-and selenoprotein-speci®c (Behne et al, 1991), which may be mediated by tissue-speci®c changes in selenocysteine tRNA:s (Diamond et al, 1993) and differences in the selenocysteine insertion sequences (SECIS) for different selenoproteins (Kollmus et al, 1996). Moreover, the response in mRNA levels of individual selenoproteins to changes in selenium supply is both tissue-speci®c and differs in magnitude and direction (Bermano et al, 1995).…”

“…At least ten different selenoproteins have been identi®ed in mammals. Their concentrations in tissues are dependent on the dietary intake of selenium (Chen et al, 1990;Behne et al, 1991;Marchaluk et al, 1995).…”

Assessment of requirements for selenium and adequacy of selenium status: a review

“…If selenomethionine is a major dietary form, then the tissue content may be high because it is nonspecifically incorporated into proteins as selenomethionine in the place of methionine (Behne et al, 1991). In blood components, selenium from organic forms but not inorganic forms, is incorporated nonspecifically into haemoglobin in erythrocytes and into albumin in plasma (Butler et al, 1991;Burk et al, 2001).…”

Haematological, Blood and Rumen Chemistry Changes in Lambs Following Supplementation with Se-yeast

“…Selenomethionine is the predominant form of selenium that occurs naturally in feedstuffs and selenized yeast. Incorporation of selenomethionine into non-specific body proteins in place of methionine (Behne et al 1991) probably explains the higher selenium concentrations in tissues and milk of ruminants that were fed organic compared with selenite selenium.…”