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At least 73 records · Page 4Linked to original sources
PubMed1990

Immunoscintigraphy with biosynthetically-labeled 75Se-antibodies--II. Comparison with antibodies labeled by radioiodination.

The biodistribution of 75Se and 125I were compared in nude mice bearing melanomas and injected simultaneously with biosynthetically-labeled 75Se-MoAbs and radioiodinated 125I-MoAbs from the same anti-melanoma hybridoma. The 75Se dose recovery in the tumor (day 10) was twice that for 125I, but the tumor to normal tissue ratios were identical. It is concluded that biosynthetically-labeled MoAbs survive better in vivo, while the tumor to normal tissue ratios are governed by the excretion rate of labeled MoAb catabolytic products.

Animals↗
PubMed1979

Uptake of selenium-75 by human lymphocytes in vitro.

Selenite uptake by human lymphocytes was studied both in whole blood and in isolated cells. When 75Se-selenite (75Se-SeO3-2--) is supplied to whole blood, it is converted by the erythrocytes to a form which rapidly becomes bound to plasma proteins. Studies with a variety of inhibitors indicated that the process is not energy dependent but that sulfhydryl groups are required. The 75Se bound to plasma proteins is absorbed by lymphocytes in preference to 75SeO3-2-. By the use of selective inhibitors (respiratory, sulfhydryl, protein biosynthetic) it was demonstrated that the uptake of either form of 75Se requires neither energy nor protein synthesis; however, all the sulfhydryl inhibitors cause a decrease of absorption. A scheme which summarizes the pathway of selenite conversion in human blood and uptake by lymphocytes is presented; the data indicate that plasma proteins function as carriers of selenium to lymphocytes.

Blood Proteins↗
PubMed1996

Molecular biological and biochemical characterization of the human type 2 selenodeiodinase.

Type 2 deiodinase (D2) is a low K(m) iodothyronine deiodinase that catalyzes the removal of a single iodine from the phenolic ring of T4 or rT3. We sequenced and subcloned the open reading frame from a partial complementary DNA (cDNA) clone (2.1 kilobases) prepared by Genethon (Z44085) from a human infant brain cDNA library. The open reading frame encodes a putative 273-amino acid protein of 31 kDa with greater than 70% similarity to the Rana catesbeiana D2 protein. Transient expression of the cDNA produces a low K(m) (5 nM for T4; 8 nM for rT3) propylthiouracil- and gold thioglucose-resistant 5'-deiodinase in 293-HEK cells. Human D2, like human type 1 (D1) and type 3 (D3) deiodinases, is a selenoenzyme, as evidenced by 1) the presence of two in-frame UGA codons (positions 133 and 266), 2) the synthesis of a 31-kDa 75Selabeled protein in D2 cDNA-transfected cells, and 3) the requirement for a 3'-selenocysteine incorporation sequence element for its translation. Unlike D1 and D3, we were not able to covalently label overexpressed D2 with N-bromoacetyl [125I]T3 or -T4. We found that the human D2 messenger RNA is 7-8 kilobases and is expressed in brain, placenta, and, surprisingly, cardiac and skeletal muscle. Type 2 deiodinase activity was also present in human skeletal muscle. These results indicate that there are unique features of D2 that distinguish it from the two other selenodeiodinases. The expression of D2 in muscle suggests that it could play a role in peripheral, as well as intracellular, T3 production.

Amino Acid Sequence↗
PubMed1991

Glycine reductase protein C. Properties and characterization of its role in the reductive cleavage of Se-carboxymethyl-selenoprotein A.

The clostridial glycine reductase complex catalyzes the reductive deamination of glycine in an energy-conserving process that results in the esterification of orthophosphate. The complex consists of three protein components: selenoprotein A; protein B, a carbonyl group protein; and protein C, a sulfhydryl protein. The protein C component also catalyzes the arsenate-dependent decomposition of acetyl phosphate. Reaction of protein C with iodoacetate inhibits its ability to decompose acetyl phosphate, but this inactivation of the enzyme by alkylation is prevented in the presence of the substrate indicating the formation of an unreactive enzyme-bound acetylthiol ester. The Se-carboxy-methylselenocysteine residue of the selenoprotein A component of glycine reductase was generated by selective alkylation of the ionized selenol group at pH 6 with [14C]bromoacetate. Using this pure alkylated selenoprotein A as substrate, it was shown that protein C catalyzes the conversion of the [14C]carboxymethyl group, in selenoether linkage to protein A, to [14C]acetate in the presence of arsenate, dithiothreitol, and Mg2+. A procedure using hydrophobic chromatographic matrices was developed for the large scale isolation of protein C, and a number of the properties of the enzyme were determined.

Alkylation↗
PubMed1994

125I-labelling of an internally 75Se-labelled monoclonal antibody--biodistribution in tumour-bearing nude mice.

A monoclonal antibody, C215, was first internally labelled with 75Se-methionine and then labelled with 125I. The biodistribution of the dual-labelled [125I][75Se]C215 was studied in tumour-bearing nude mice killed 3 days after injection. The biodistribution of the dual-labelled [125I][75Se]C215 was compared with the biodistribution of single-labelled [131I]C215 and [75Se]C215. Iodine-labelled antibodies seem to be damaged during iodination, affecting the disappearance rate and tumour uptake. There were no signs of dehalogenation of circulating antibodies or antibodies taken up in the tumour.

Adenocarcinoma↗
PubMed1983

Specific incorporation of selenium into lysine- and glutamate- accepting tRNAs from Escherichia coli.

Amino acid transfer nucleic acids (tRNAs) that contain selenium-modified bases are synthesized by Escherichia coli in the presence of low levels (0.1-0.5 microM) of [75Se]selenite or [75Se]selenate. The amount of selenium incorporated (1-2 g atoms/100 mol of tRNA) was unchanged by 10-20-fold variations in selenium or sulfate concentrations or by the addition of 1 mM cysteine, sulfide, or sulfite. Specific incorporation of selenium (as opposed to nonspecific substitution for sulfur) was further indicated by the different reversed phase chromatographic elution patterns of 35S- and 75Se-labeled tRNAs isolated from cells labeled with 35SO2-4 and 75SeO2-4. Also, E. coli mutants unable to synthesize an abundant sulfur-modified base, 4-thiouracil, nevertheless produced normal levels of selenium-modified tRNAs. Two different methods of distinguishing between aminoacylated and nonaminoacylated tRNA, one which examined mobility during reversed phase chromatography and another which employed anti-AMP antibodies, indicated that over 50% of the selenium-containing tRNA had lysine or glutamate acceptor activity.

Escherichia coli↗