Separation of 44Ti from proton irradiated scandium by using solid-phase extraction chromatography and design of 44Ti/44Sc generator system.

Scandium-44g (half-life 3.97h [1]) shows promise for positron emission tomography (PET) imaging of longer biological processes than that of the current gold standard, 18F, due to its favorable decay parameters. One source of 44gSc is the long-lived parent nuclide 44Ti (half-life 60.0 a). A 44Ti/44gSc generator would have the ability to provide radionuclidically pure 44gSc on a daily basis. The production of 44Ti via the 45Sc(p,2n) reaction requires high proton beam currents and long irradiation times. Recovery and purification of no-carrier added (nca) 44Ti from scandium metal targets involves complex separation chemistry. In this study, separation systems based on solid phase extraction chromatography were investigated, including branched diglycolamide (BDGA) resin and hydroxamate based ZR resin. Results indicate that ZR resin in HCl media represents an effective 44Ti/44gSc separation system.

Control of Escherichia coli superoxide dismutase (sodA and sodB) genes by the ferric uptake regulation (fur) locus.

The ferric uptake regulation (fur) gene product participates in regulating expression of the manganese- and iron-containing superoxide dismutase genes of Escherichia coli. Examination of beta-galactosidase activity coded from a chromosomal phi(sodA'-'lacZ) fusion suggests that metallated Fur protein acts as a transcriptional repressor of sodA (manganese superoxide dismutase [MnSOD]). Gel retardation assays demonstrate high-affinity binding of pure, Mn2(+)-Fur protein to DNA fragments containing the sodA promoter. These data and the presence of an iron box sequence in its promoter strongly suggest that sodA is part of the iron uptake regulon. An sodB'-'lacZ fusion gene borne on either a low- or high-copy plasmid yielded approximately two- to threefold more beta-galactosidase activity in Fur+ compared with Fur- cells; the levels of activity depended only weakly on the growth phase and did not change during an extended stationary phase. Measurement of FeSOD activity in logarithmic growth phase and in overnight cultures of sodA and fur sodA backgrounds revealed that almost no FeSOD activity was expressed in Fur- strains, whereas wild-type levels were expressed in Fur+ cells. Fur+ and Fur- cells bearing the multicopy plasmid pHS1-4 (sodB+) expressed approximately sevenfold less FeSOD activity in the fur background, and staining of nondenaturing electrophoretic gels indicates that synthesis of FeSOD protein was greatly reduced in Fur- cells. Gel retardation assays show that Mn2(+)-Fur had a significantly higher affinity for the promoter fragment of sodB compared with that of random DNA sequences but significantly lower than for the promoter fragment of sodA. These observations suggest that the apparent positive regulation of sodB does not result exclusively from a direct interaction of holo (metallated) Fur itself with the sodB promoter. Nevertheless, the sodB gene also appears to be part of the iron uptake regulon but not in the classical manner of Fe-dependent repression.

Characterization of metal binding peptides from cadmium resistant plant cells.

The majority of the cellular cadmium (less than 80%) in cadmium resistant Datura innoxia cells is bound to a small, metal induced peptide which is not metallothionein. This peptide consists of glutamate, cysteine and glycine in a ratio between 2:2:1 and 3:3:1 and has an apparent molecular weight of 776, under denaturing conditions. It is heat stable and complexes with cadmium to produce multimeric forms which are separable by gel filtration. Chemical analyses suggest that some amino acids are not joined by classical peptide linkages. This indicates that the synthesis of the peptide may not be directed by mRNA and that induction of its synthesis may not involve increased transcription from a putative gene corresponding directly to this peptide. A smaller proportion (greater than 15%) of the cellular cadmium is bound to a larger compound which is also heat stable and binds copper more readily than cadmium in vivo. This larger compound has an amino acid composition similar, in some respects, to metallothioneins.

Selection, Isolation, and Characterization of Cadmium-Resistant Datura innoxia Suspension Cultures.

Datura innoxia cells from suspension cultures were selected for their ability to grow and divide rapidly in normally lethal concentrations of cadmium. Cells resistant to 12.5, 25, 50, 100, 160, 200, and 250 micromolar cadmium chloride were isolated and utilized to initiate cell suspension cultures resistant to this toxic metal ion. Variant cell lines retained their ability to grow in cadmium after being grown in its absence for more than 400 generations. Resistance to cadmium was correlated with the synthesis of low molecular weight, cysteine-rich, cadium-binding proteins. Synthesis of these proteins was induced rapidly in cadmium-resistant cells in response to a challenge of cadmium. Induction was detectable within one hour after exposure of the cells to the metal ion. Accumulation of protein bound cadmium reached a maximum eight to twelve hours following exposure. Metal-binding proteins were not detectable in the cadmium sensitive D. innoxia cells from which resistant cells were derived.