Zeta potentials of the rare earth element fluorcarbonate minerals focusing on bastnäsite and parisite.

Rare earth elements (REE) are critical to a wide range of technologies ranging from mobile phones to wind turbines. Processing and extraction of REE minerals from ore bodies is, however, both challenging and relatively poorly understood, as the majority of deposits contain only limited enrichment of REEs. An improved understanding of the surface properties of the minerals is important in informing and optimising their processing, in particular for separation by froth flotation. The measurement of zeta potential can be used to extract information regarding the electrical double layer, and hence surface properties of these minerals. There are over 34 REE fluorcarbonate minerals currently identified, however bastnäsite, synchysite and parisite are of most economic importance. Bastnäsite-(Ce), the most common REE fluorcarbonate, supplies over 50% of the world's REE. Previous studies of bastnäsite have showed a wide range of surface behaviour, with the iso-electric point (IEP), being measured between pH values of 4.6 and 9.3. In contrast, no values of IEP have been reported for parisite or synchysite. In this work, we review previous studies of the zeta potentials of bastnäsite to investigate the effects of different methodologies and sample preparation. In addition, measurements of zeta potentials of parisite under water, collector and supernatant conditions were conducted, the first to be reported. These results showed an iso-electric point for parisite of 5.6 under water, with a shift to a more negative zeta potential with both collector (hydroxamic and fatty acids) and supernatant conditions. The IEP with collectors and supernatant was <3.5. As zeta potential measurements in the presence of reagents and supernatants are the most rigorous way of determining the efficiency of a flotation reagent, the agreement between parisite zeta potentials obtained here and previous work on bastnäsite suggests that parisite may be processed using similar reagent schemes to bastnäsite. This is important for future processing of REE deposits, comprising of more complex REE mineralogy.

Theoretical and experimental tests of a chromosomal fingerprint for densely ionizing radiation based on F ratios calculated from stable and unstable chromosome aberrations.

In the present study, F ratios for both stable chromosome aberrations, i.e. ratios of translocations to pericentric inversions, and unstable aberrations, i.e. dicentrics and centric rings, were measured using fluorescence in situ hybridization. F ratios for stable aberrations measured after exposure to low (2.89 Gy 60Co gamma rays) and high-LET (0.25 Gy 56Fe ions; 1.25 Gy 56Fe ions; 3.0 Gy 12C ions) radiation were 6.5 +/- 1.5, 4.7 +/- 1.6, 9.3 +/- 2.5 and 10.4 +/- 3.0, respectively. F ratios for unstable aberrations measured after low (2.89 Gy 60Co gamma rays) and high-LET (0.25 Gy 56Fe ions; 3.0 Gy 12C ions) radiations were 6.5 +/- 1.6, 6.3 +/- 2.3 and 11.1 +/- 3.7, respectively. No significant difference between the F ratios for low- and high-LET radiation was found. Further tests on the models for calculation of the F ratio proposed by Brenner and Sachs (Radiat. Res. 140, 134-142, 1994) showed that the F ratio may not be straightforward as a practical fingerprint for densely ionizing radiation.

Alpha coefficient of dose-response for chromosome translocations measured by FISH in human lymphocytes exposed to chronic 60Co gamma rays at body temperature.

PURPOSE: To measure the alpha coefficient, the initial slope of the translocation dose-response curve, for 60Co gamma-rays in human lymphocytes. MATERIALS AND METHODS: Human lymphocytes were exposed to 0, 0.32, 0.62 and 0.92 Gy of chronic 60Co gamma-rays under conditions that reduce the metabolic stress to the cells. Chromosome translocation frequencies were measured using fluorescence in situ hybridization with a whole-chromosome probe cocktail specific for chromosomes 1, 2, 4 (orange) and 3, 5, 6 (green). RESULTS: A total of 72,383 metaphases were analysed (33,429 in exposed cells) in two individuals. The shape of the dose-response curves for translocations was linear, and alpha coefficient was measured as 0.024 +/- 0.002 translocations per cell per Gy for the combined data for two 24 year old male donors. CONCLUSION: The alpha coefficients measured after chronic exposure were in good agreement with that reported in the literature for acute, low-dose exposure of human lymphocytes to 60Co gamma-rays.

Site-specific core 1 O-glycosylation pattern of the porcine submaxillary gland mucin tandem repeat. Evidence for the modulation of glycan length by peptide sequence.

The sequence-specific O-linked core 1 ([R1, R2]-beta-Gal(1-3)-alpha-GalNAc-O-Ser/Thr) glycosylation pattern has been quantitatively determined for 30 of the 31 Ser/Thr residues in the 81-residue porcine submaxillary gland mucin tandem repeat. This was achieved by Edman amino acid sequencing of the isolated tandem repeat after selective removal of non-C3-substituted, peptide-linked GalNAc residues by periodate oxidation and subsequent trimming of the remaining oligosaccharides to peptide-linked GalNAc residues by mild trifluoromethanesulfonic acid/anisole treatment. The sequencing reveals 61% (range, 12-95%) of the peptide alpha-N-acetylgalactosamine (GalNAc) residues to be substituted by core 1 chains, a value in agreement with the carbon-13 NMR analysis of the native mucin. Residues with the lowest C3 substitution were typically clustered in regions of sequence with the highest densities of (glycosylated) serine or threonine. This suggests that the porcine beta3-Gal, core 1, transferase is sensitive to peptide sequence and/or neighboring core GalNAc glycosylation in vivo, in keeping with earlier in vitro enzymatic glycosylation studies (Granovsky, M., Blielfeldt, T., Peters, S., Paulsen, H., Meldal, M., Brockhausen, J., and Brockhausen, I. (1994) Eur. J. Biochem. 221, 1039-1046). These results demonstrate that the O-glycan structures in mucin domains are not necessarily uniformly distributed along the polypeptide core and that their lengths can be modulated by peptide sequence. The data further suggest that hydroxyamino acid spacing may contribute to the regulation of glycan length, thereby, providing a mechanism for maintaining an optimally expanded, protease resistant, mucin conformation.

Determination of the site-specific O-glycosylation pattern of the porcine submaxillary mucin tandem repeat glycopeptide. Model proposed for the polypeptide:galnac transferase peptide binding site.

The heterogeneously glycosylated 81-residue tryptic tandem repeat glycopeptide from porcine submaxillary mucin (PSM) has been isolated and its glycosylation pattern determined by amino acid sequencing. Key to these studies is the ability to trim the structurally heterogeneous PSM oligosaccharide side chains to homogeneous GalNAc monosaccharide side chains by mild trifluoromethanesulfonic acid treatment. Trypsin treatment of trifluoromethanesulfonic acid-treated PSM releases the 81-residue tandem repeat as an ensemble of 81-residue glycopeptides with different glycosylation patterns. Automated amino acid sequencing using Edman degradative chemistry of the repeat was used to determine the extent of glycosylation of nearly every Ser and Thr residue. The Thr residues are all highly glycosylated within the range of 73-90%, giving an average Thr glycosylation of 83%. In contrast, the Ser residues display a wide range of glycosylations, ranging between 33 and 95%, giving an average Ser glycosylation of 74%. These data are consistent with the known elevated glycosylation of Thr peptides over Ser peptides for the porcine UDP-N-acetylgalactosamine:polypeptide N-acetylgalactosaminyltransferase. It is also observed that the extent of glycosylation of the repeat correlates poorly with published predictive methods. An examination of the sequences surrounding the glycosylation sites reveals that nearly all of the highly glycosylated sites have a penultimate Gly residue, whereas those that are less highly glycosylated have medium to large side chain penultimate residues. As observed by others, glycosylation also appears to be modulated by the presence of Pro residues. On the basis of these findings we suggest that the acceptor peptide binds the transferase in a beta-like conformation and that penultimate residue side chain steric interactions may play a role in determining extent that a given Ser or Thr is glycosylated. A model for the GalNAc transferase peptide binding site is proposed.

Characterization of the 46,000-dalton subunit of eIF-4F.

Three protein synthesis initiation factors, eukaryotic initiation factor (eIF)-4A, -4B, and -4F are required for the ATP-dependent binding of mRNA to the ribosome. To extend the characterization of the eIF-4A-like subunit of eIF-4F, a cDNA clone encoding eIF-4A has been isolated from a rabbit liver cDNA library and sequenced. The clone is almost full length for the coding region and complete for the 3' noncoding region. The sequence of the rabbit cDNA has been compared to the sequence of the two similar, but not identical, genes and cDNAs encoding mouse eIF-4A (termed eIF-4AI and eIF-4AII). The rabbit cDNA sequence is very similar to the mouse eIF-4AI genomic and liver cDNA sequence with 100% identity at the amino acid level and 90% identity at the nucleotide level within the protein coding region; however, there is very little similarity in the 3' noncoding region. Amino acid sequencing of purified rabbit reticulocyte eIF-4A protein indicates that it is eIF-4AI (encoded by the eIF-4AI gene and cDNA) and none of the amino acid residues sequenced are in disagreement with those predicted from the mouse liver or rabbit liver cDNA sequences. Subsequently, we have analyzed the p46 subunit of eIF-4F, a three subunit protein whose molecular weights have been estimated by sodium dodecyl sulfate gel electrophoresis to be 220,000, 46,000 and 24,000. The p46 subunit has physical properties similar to eIF-4A. This subunit was isolated from rabbit reticulocyte eIF-4F and sequenced chemically. Our results indicate that this peptide is a mixture of eIF-4AI and eIF-4AII in an approximate ratio of 4 to 1, respectively. No eIF-4AII was observed in our rabbit reticulocyte eIF-4A preparation. Therefore we have concluded that either the eIF-4AI and the eIF-4AII proteins were resolved from each other in the purification of rabbit reticulocyte eIF-4A or that eIF-4AII preferentially associates with the p220 and p24 subunits of eIF-4F. Evidence favoring the latter possibility is discussed.

Characterization of protein synthesis factors from rabbit reticulocytes.

As part of our efforts to characterize eukaryotic translation factors, we have sequenced a number of them chemically and inferred sequences from cDNA clones. To our surprise, there appears to be extensive identity of amino acid sequence in most factors characterized to date in that within mammalian species, usually greater than 99% identity is observed. Extreme examples are rabbit EF-1 alpha which is 100% identical to human EF-1 alpha and rabbit eIF-4AI and eIF-4AII which are 100% identical to mouse eIF-4AI and eIF-4AII for those amino acids sequenced (398/406 and 156/407, respectively). An extended analysis has been made of EF-1 alpha which in rabbit has three different post-translational modifications, dimethyllysine, trimethyllysine and glycerylphosphorylethanolamine. A comparison of the primary structure of EF-1 alpha to E. coli EF-Tu indicates an overall sequence identity of 33%. However, within the amino terminal 180 amino acids (the GTP-binding domain), there are found regions of much greater identity (50/85 = 59%).

Location of seven post-translational modifications in rabbit elongation factor 1 alpha including dimethyllysine, trimethyllysine, and glycerylphosphorylethanolamine.

Amino acid sequencing of a large number of chemical and enzymatic cleavage products of elongation factor 1 alpha purified from rabbit reticulocyte has identified seven post-translationally modified residues. Five of the modifications are methylations of lysine residues yielding dimethyllysine at residues 55 and 165 and trimethyllysine at residues 36, 79, and 318. The two remaining post-translational modifications involve the addition of ethanolamine to glutamic acid residues 301 and 374, as reported previously (Rosenberry, T. L., Krall, J. A., Dever, T. E., Haas, R., Louvard, D., and Merrick, W. C. (1989) J. Biol. Chem. 264, 7096-7099). Fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry have been used to analyze peptides containing these modified residues. The analyses have determined that glycerylphosphorylethanolamine has been attached to the glutamic acid residues. An analysis of the amino acid sequence surrounding each of the three types of modification has indicated no similarities. Therefore, it seems likely that the modifying enzymes do not recognize a specific amino acid sequence but rather the three-dimensional presentation of either amino or carboxyl residues in the elongation factor 1 alpha structure.