Biologie und Biochemie des Elements Selen

The importance of selenium as an essential trace element has progressively emerged during the last years due to the analysis of selenium deficiency diseases and to the identification and characterization of a number of selenoenzymes. Selenium is incorporated in the catalytic site of the enzymes as an integral selenocysteine residue. The pathway of selenocysteine biosynthesis and incorporation has been elucidated recently for Escherichia coli. This article presents an overview on these subjects and describes the mechanisms which confer selenocysteine specificity in the framework of protein biosynthesis. In addition, some considerations concerning the phylogeny of selenocysteine incorporation are presented and a model for the evolution of the selenocysteine pathway is proposed.     

A polyiodide with regular I 4 2− chains: Tl6PbI10

The Science of Nature -     

Prenatal diagnosis of mosaic 4p – in a fetus with trisomy 21

Mosaicism for the Wolf-Hirschhorn syndrome, del(4)(p16), is extremely rare and has not been reported in association with a numerical chromosome abnormality. We report the prenatal diagnosis of mosaic del(4)(p16) and non-mosaic trisomy 21 in a 16-week female fetus. The pregnancy ended in spontaneous abortion at 34 weeks secondary to fetal demise. The fetus had features of both 4p – and trisomy 21.     

Quantification of human amniotic fluid constituents by high resolution proton nuclear magnetic resonance (NMR) spectroscopy

We have investigated the ability of high-resolution proton NMR spectroscopy to provide a biochemical constituent screening of human amniotic fluid (AF). Proton NMR spectra were obtained at 300 MHz on AF from patients undergoing amniocentesis in the mid-trimester. Only AF from normal pregnancies (normal fetal karyotype, normal a-fetoprotein levels, normal birth outcome) was used in this study. The AF supernatant was lyophilized and resuspended in deuterated water containing 0.1 mm phosphate buffer and 6.02 mm disodium maleate. Identification of low molecular weight compounds was confirmed by two-dimensional NMR spectra (primarily correlated spectroscopy, or COSY) and standard addition techniques. A broad profile of compounds were ‘NMR visible’ in a single proton spectrum, including creatinine, glucose, organic acids (acetate, citrate, and lactate) and several amino acids (alanine, histidine, leucine, phenylalanine, tyrosine and valine). The proton spectrum was unaffected by prior freezing/thawing of AF samples. We were able to quantify compounds by comparison with an added concentration standard (maleate) at concentrations as low as 30 μm. Good agreement with literature values based on other analytical techniques was obtained.