Cadmium-binding peptides from plants.
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Cadmium↗
Biomedical subjects
W E Rauser
Publications and source records attributed to W E Rauser.
The Cd-binding protein from tomato compared to those of other vascular plants.
Cd-binding protein from tomato roots was partially purified and characterized. The Cd-protein complex was eluted as a single Cd peak from QAE-Sephadex A-25 and purified further on Sephadex G-75 in 1 M KC1 buffer. Circular dichroism measurements showed positive Cotton bands at 232 and 273 nm and a negative band at 253 nm, indicative of Cd-thiolate coordination. The major amino acids were Cys (25.6%), Glx (53.3%), Asx (5.4%) and Gly (12.8%) with no aromatic residues detected. The Cd:Cys ratio was 1:2.4. The material had an apparent molecular mass of 3,000 daltons on gel filtration through Sephadex G-50 fine in 1 M KC1 buffer. The tomato protein resembled the Cd-binding proteins isolated from black bentgrass, maize and cabbage. The presence of Cd-thiolate coordination and the high content of Cys are critical features typical of metallothioneins. The abundance of Glx creates a highly anionic protein which is unlike animal metallothioneins. It is proposed that the Cd-binding proteins from vascular plants be designated phytometallothioneins.
Amino Acids↗
Ribosomal complexes from an extremely halophilic bacterium and the role of cations.
Concentrated extracts of Halobacterium cutirubrum were prepared at 0 C by gently disrupting cells with a nonionic detergent in a medium containing 3.0 m KCl, 0.5 m NH(4)Cl, and 0.04 m (or more) magnesium acetate and then treating the gelatinous mass with deoxyribonuclease. On KCl-sucrose gradients containing 0.5 m NH(4)Cl and 0.04 m magnesium acetate, these extracts showed 30S and 50S ribosomal subunits plus a flat profile of faster-sedimenting material up to high S values. Only after frozen storage or brief incubation of the extract were 70S ribosomes and distinct classes of small polyribosomes detected. Digestion with ribonuclease converted faster-sedimenting material to 70S particles. The presence of chloramphenicol during preparation of the extracts did not affect these results. The evidence suggests that ribosomal particles exist in these cells as subunits or as polyribosomes but not as 70S ribosomes. To investigate the function of Mg(++) and NH(4) (+) ions in ribosomal complexes from this halophile, concentrated cell extracts and extracts incubated with (14)C-leucine were examined on KCl-sucrose gradients containing different concentrations of these ions. Polyribosomes and the bulk of 70S ribosomes dissociated reversibly to subunits at about 0.01 m Mg(++), whereas a small fraction of the 70S particles, including those which in vitro incorporated (14)C-leucine into nascent protein, dissociated only below 1 mm Mg(++). Below this concentration of Mg(++), nascent protein remained attached to the 50S subunit even at 0.04 mm Mg(++) in the presence of 0.35 to 0.5 m NH(4)Cl. Nascent protein, presumably as peptidyl-transfer ribonucleic acid, dissociated reversibly from 50S subunits only at 0.04 mm Mg(++) and 0.1 m or less NH(4) (+). Thus, the stability of polyribosomes from H. cutirubrum depends specifically on both Mg(++) and NH(4) (+) ions.
Ammonium Chloride↗