J.T. Deagen

Uptake of selenite, selenomethionine and selenate by brush border membrane vesicles isolated from rat small intestine

The uptake of selenite, selenate and selenomethionine (SeMet) was performed with brush border membrane vesicles (BBMV) prepared from rats fed selenium-deficient and supplemented diets. At equilibrium (60 min), the uptake of 75Se from [75Se]selenite ranged from 16.5 to 18.9 nmol mg-1 protein. There was a curvilinear relationship in the uptake of selenite over a concentration range of 10–1000 μm. About 2 nmol mg-1 protein was obtained with selenomethionine (SeMet) which occurred between 90 and 180 s. In contrast to selenite, there was a linear relationship in the initial uptake of SeMet over a concentration range of 10–1000 μm. The uptake of selenate was approximately 50-fold lower than selenite, reaching 350 pmol mg-1 protein. Dietary selenium level had no effect on the rate of 75Se accumulation by BBMV. Dramatic differences are found in the uptake and binding of selenium by BBMV incubated with different selenocompounds.

Chemical forms of selenium in selenium containing proteins from human plasma

The chemical forms of selenium (Se) were determined in human plasma fractions. Human plasma was subjected to gel filtration using Sephadex G-150, and the first Se peak from this column was subsequently chromatographed on DEAE-Sephacel. The form of Se in the Se peak which eluted from this column was shown to be selenocysteine (SeCys). In a second approach human plasma was again subjected to gel filtration and the first Se peak was chromatographed on Affigel blue. SeCys was shown to be the form of Se in both the retained and unretained Se on this column. The second gel filtration Se peak was also chromatographed on Reactive Blue 2-Sepharose CL-6B and the form of Se which was not retained was also shown to be SeCys. However, the form which was retained was shown to be selenomethionine. Evidence is presented that there are three Se containing proteins in human plasma, which are selenoprotein P, glutathione peroxidase, and albumin.

Biological function of metallothionein-IV. Biosynthesis and degradation of liver and kidney metallothionein in rats fed diets containing zinc or cadmium

The half-lives of liver and kidney metallothionein of rats fed diets containing either 2,000 ppm Zn or 100 ppm Cd were determined by a single injection of 14C-cystine. This protein was purified by Sephadex G-75 and DEAE cellulose column chromatography. Half-lives of liver metallothionein in rats fed the basal (18 ppm Zn), high Zn (2,000 ppm Zn), high Zn then basal, and high Cd (100 ppm) diet were, respectively, 3.4, 2.7 1.3, and 3.3 days, and that of kidney metallothionein were, respectively, 2.0, 2.2, 1.4, and 3.6 days. Thus, Cd-thionein has a longer half-life than Zn-thionein in both liver and kidney. The major species of metallothionein, which were separated on DEAE cellulose, had similar half-lives. Metallothionein, a protein having high content of metals and relatively short half-life, is possibly involved in cellular regulatory function.

Uptake of selenotrisulfides of gluthathione and cysteine by brush border membranes from rat intestines

The uptake of selenodiglutathione and selenodicysteine was compared to that of selenite by brush border membrane vesicles (BBMV) prepared from rat intestinal tracts. It was found that it is critical to maintain a pH of 6.0 or below to prevent the spontaneous breakdown of these compounds. When conducted at pH 6.0, the uptake of selenodiglutathione and selenodicysteine was more than ten times faster than for selenite selenium. Ligated intestinal loop studies were conducted to determine if similar results would be obtained in vivo. In comparison to selenite, selenium absorption was enhanced 68% and the transfer to the body increased 2.4-fold when selenium as selenodiglutathione was placed in the ileum. The absorption of selenium as selenodicysteine was increased by 57% and the transfer doubled in comparison to selenite when placed in the ileum. Thus, the stimulated absorption of selenite by glutathione or cysteine appears to be through the formation of complexes with these compounds.

Tissue metallothionein: dietary interaction of cadmium and zinc with copper, mercury, and silver

The interaction of dietary Cd and Zn with Cu, Hg, and Ag in relation to tissue metallothionein (MT) was studied with rats. Dietary Cd was found to increase the deposition of Cu and Ag in liver and kidney MT. Cd also caused accumulation of Hg in liver MT but depletion of Hg in kidney MT. In contrast to Cd, high dietary levels of Zn had no influence on the deposition of these metals in MT when they were included in the diet. When Zn was fed in the diet and Cu, Cd, Hg, and Ag were injected into rats, Zn caused increased deposition of these metals in MT, suggesting an interaction at the intestinal level. Hg and Cd were distributed between the two species of MT, but Cu was found predominantly in one of the MT species. Evidence was obtained that Ag was bound to a different MT species than Hg, Cu, or Cd when included in the diet containing Cd.

Biological function of metallothionein. VI. Metabolic interaction of cadmium and zinc in rats

The accumulation and depletion of cadmium in liver and kidney metallothionein (MT) and the effects of dietary zinc deficiency on cadmium metabolism were studied in rats. The accumulation of cadmium in liver MT started to plateau after 80 days, but there was a linear accumulation of this element in kidney MT over the entire 300-day experiment. Cadmium in MT fractions was depleted very slowly when rats were changed to a diet without cadmium. The accumulation of cadmium in MT also caused zinc to accumulate in this protein, even in rats fed zinc-deficient diets. However, the reverse situation was found not to be true; zinc did not cause cadmium to accumulate in MT. Dietary zinc deficiency limited the binding of injected109Cd to MT of liver, but not of kidneys or testes. However, zinc-deficient rats fed cadmium in their diets metabolized cadmium similarly to zinc-supplemented rats, suggesting that zinc deficiency does not limit the ability of cadmium to stimulate MT synthesis.

Zinc, Iron, Copper, Selenium, Lactoferrin, and Ferritin in Human Pus

Background: Restriction of zinc and iron available for microbial growth in tissues are well‐recognized host defense mechanisms. The present studies were performed to characterize some constituents of human pus that may affect these important host defenses. Methods: Zinc, iron, copper, calcium, and magnesium in pus were measured using an atomic absorption spectrophotometer; selenium was measured fluorometrically. Ferritin was measured with a fluorometric enzyme immunoassay, and lactoferrin was measured with a radial diffusion assay. The growth of Escherichia coli at 37°C was measured in pus supernate adjusted to pH 5.5 or 7.4, in boiled supernate, or in supernate adjusted with 1.3 mM iron or 0.9 mM zinc singly or together. Results: Zinc and iron concentrations in pus exceeded normal serum. Calcium and magnesium levels were 2‐ to 3‐fold lower and higher, respectively, than normal serum values. Lactoferrin concentrations of were 880 ± 48 &mgr;g/mL and ferritin levels were 20,726 ± 2,667 ng/mL. Growth of an E coli strain was inhibited in pus at pH 5.5 but not at pH 7.4, and growth was enhanced by addition of iron or zinc to E coli suspended in pus at pH 6.7. Conclusions: To our knowledge, this is the first report of the zinc, iron, copper, selenium, lactoferrin, and ferritin levels of human pus. These studies provide additional insight into host defense mechanisms mediated by the restriction of the bioavailability of zinc and iron in suppurative infection.

Bioavailability to rats of selenium in ovine muscle, liver and hemoglobin

Abstract Muscle, liver and hemoglobin from sheep which had been fed a high selenium (Se) diet (1 mg Se/kg) were incorporated into diets for rats at levels of 0.05, 0.1 and 0.15 μg Se per g diet. Se as either selenite or L-selenomethionine (SeMet) were used as standards at these same levels to obtain information on the most suitable reference. Tissue Se levels and glutathione peroxidase activities were used to assess bioavailability. Se was found to be more available in muscle than liver or hemoglobin.

Low Molecular Weight Cadmium and Selenium Containing Proteins unlike Metallothionein in Animals

Since the assumed metallothionein (MT) fractions from testis did not respond to cadmium and zinc exposure like MT in other tissues, they were purified using gel filtration and ion exchange resins to determine if they were indeed MT or other proteins. The major amino acids were found to be aspartate, glutamate and glycine with a low cysteine (less than 3%) content. The amino acid content is remarkably similar to a low molecular weight (MW) cadmium-binding protein isolated from oysters with properties unlike MT. Selenium has been shown to be present in a low MW protein called the G protein in various tissues including the testis. The major amino acids in a partially purified preparation were found to be aspartate, glutamate, glycine and lysine with a low methionine (about 2.5%) but a very low cysteine (less than 0.3%) content. The selenium is present in this protein as selenocysteine. The metabolic significance of this selenoprotein is not known, but it should be indicated that selenium will alter the binding of cadmium in testicular proteins.

Influence of zinc on copper binding in tissue proteins of steers

Two experiments were conducted with steers fed diets containing 270 ppm copper either with or without 2050 ppm zinc. Liver biopsies were taken from steers biweekly for 10 wk for analysis. The steers were then killed; tissues were removed, homogenized, and centrifuged, and the pellets were extracted with mercaptoethanol (BME), and selected cytosols and extracts were subjected to gel filtration (Sephadex G-75). Copper and zinc were determined on the BME extracts, pellets after extraction, cytosols, and gel-filtration fractions. Copper accumulated at about the same rate in BME extract and in the extracted pellet, with the smallest amount in the cytosol. In contrast, over 70% of the zinc was present in the hepatic cytosols. Gel filtration of BME extracts revealed the greatest amount of copper in a low-molwt (MW) peak in addition to three minor peaks of copper. Within the hepatic cytosols, the greatest amount of copper accumulated in proteins of MW>75,000, the next greatest amount in 30,000-MW proteins, and the least amount with metallothionein (MT) of steers fed the diet with only copper added. In contrast, the greatest amount of copper was present with MT in hepatic cytosols of the steer fed a diet that included copper plus zinc. Hence the zinc status of steers influences the deposition of copper in the cytosolic proteins (as demonstrated by liver, kidney, and pancreas), but not in the intracellular fractions.