Affiliations: Division of Gastroenterology, Department of Medicine
and Clinical Nutrition Research Unit, Vanderbilt University School of Medicine,
Nashville, TN 37221, USA
Note: [] C-2104, Medical Center North, Vanderbilt Medical Center,
Nashville, TN 37232-2279, USA. Tel.: +1 615 343 7740; Fax: +1 615 343 6229;
E-mail: [email protected]
Abstract: Selenium is present in plasma and tissues in specific and
non-specific forms. The experiments reported here were carried out to clarify
some factors that affect these forms of the element in plasma. A
selenium-replete human subject was given 400 μg of
selenium daily for 28 days as selenomethionine and, in a separate experiment,
as selenate. The selenomethionine raised plasma and albumin selenium
concentrations. Selenate did neither. The molar ratio of methionine to selenium
in albumin was approximately 8000 under basal and selenate-supplemented
conditions but 2800 after selenomethionine supplementation. This demonstrates
that selenium from selenomethionine, but not selenium from selenate, can be
incorporated into albumin, presumably as selenomethionine in the methionine
pool. Selenocysteine incorporation into albumin was studied in rats using
^{75}Se-selenocysteine. No evidence was obtained for
incorporation of ^{75}Se into albumin after exogenous
administration or endogenous synthesis of
^{75}Se-selenocysteine. Thus, selenocysteine does not appear
to be incorporated non-specifically into proteins as is selenomethionine. These
findings are in support of selenomethionine being a non-specific form of
selenium that is metabolized as a constituent of the methionine pool and is
unaffected by specific selenium metabolic processes. No evidence was found for
non-specific incorporation of selenium into plasma proteins when it was
administered as selenate or as selenocysteine. These forms of the element
appear to be metabolized by specific selenium metabolic processes.
