Morphology, structure, and metal binding mechanisms of biogenic manganese oxides in a superfund site treatment system.

Manganese oxides, which may be biogenically produced in both pristine and contaminated environments, have a large affinity for many trace metals. In this study, water and Mn oxide-bearing biofilm samples were collected from the components of a pump and treat remediation system at a superfund site. To better understand the factors leading to their formation and their effects on potentially toxic metal fate, we conducted a chemical, microscopic, and spectroscopic characterization of these biofilm samples. Scanning electron microscopy revealed the presence of Mn oxides in close association with biological structures with morphologies consistent with fungi. X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) revealed the oxides to be a mixture of layer and tunnel structure Mn(iv) oxides. In addition, XAS suggested that Ba, Co, and Zn all primarily bind to oxides in the biofilm in a manner that is analogous to synthetic or laboratory grown bacteriogenic Mn oxides. The results indicate that Mn oxides produced by organisms in the system may effectively scavenge metals, thus highlighting the potential utility of these organisms in designed remediation systems.

T cell receptor assembly and expression in the absence of calnexin.

Most subunits of the alphabeta deltaepsilon gammaepsilon zetazeta T cell antigen receptor (TCR) complex associate with the molecular chaperone calnexin shortly after their synthesis in the endoplasmic reticulum, including clonotypic TCRalpha,beta molecules and invariant CD3gamma,delta,epsilon chains. While calnexin interaction is suggested to be important for the stability of newly synthesized TCRalpha subunits, the role of calnexin in the survival and assembly of remaining TCR components is unknown. Here we evaluated the expression of TCR proteins in CEM T cells and the calnexin-deficient CEM variant CEM.NK(R). We found that CEM and CEM.NK(R) cells constitutively synthesized all TCR subunits except for TCRalpha and that CD3gamma,delta,epsilon components and CD3-beta complexes were effectively assembled together in both cell types. The stability and folding of core CD3epsilon chains were similar in CEM and CEM.NK(R) cells. Interestingly, TCRalpha synthesis was differentially induced by phorbol myristate acetate treatment in CEM and CEM.NK(R) cells and TCRalpha proteins synthesized in CEM.NK(R) cells showed reduced survival compared to those made in CEM cells. Importantly, these data show that TCR complexes were inducibly expressed on CEM.NK(R) cells in the absence of calnexin synthesis. These results demonstrate that TCR complexes can be expressed in the absence of calnexin and suggest that the role of calnexin in the quality control of TCR assembly is primarily restricted to the stabilization of newly synthesized TCRalpha proteins.

Modification of the T cell antigen receptor (TCR) complex by UDP-glucose:glycoprotein glucosyltransferase. TCR folding is finalized convergent with formation of alpha beta delta epsilon gamma epsilon complexes.

Most T lymphocytes express on their surfaces a multisubunit receptor complex, the T cell antigen receptor (TCR) containing alpha, beta, gamma, delta, epsilon, and zeta molecules, that has been widely studied as a model system for protein quality control. Although the parameters of TCR assembly are relatively well established, little information exists regarding the stage(s) of TCR oligomerization where folding of TCR proteins is completed. Here we evaluated the modification of TCR glycoproteins by the endoplasmic reticulum folding sensor enzyme UDP-glucose:glycoprotein glucosyltransferase (GT) as a unique and sensitive indicator of how TCR subunits assembled into multisubunit complexes are perceived by the endoplasmic reticulum quality control system. These results demonstrate that all TCR subunits containing N-glycans were modified by GT and that TCR proteins were differentially reglucosylated during their assembly with partner TCR chains. Importantly, these data show that GT modification of most TCR subunits persisted until assembly of CD3alpha beta chains and formation of CD3-associated, disulfide-linked alpha beta heterodimers. These studies provide a novel evaluation of the folding status of TCR glycoproteins during their assembly into multisubunit complexes and are consistent with the concept that TCR folding is finalized convergent with formation of alpha beta delta epsilon gamma epsilon complexes.

Low-iodine tube-feeding diet for iodine-131 scanning and therapy.

Optimal preparation for I-131 scanning and therapy of differentiated thyroid carcinoma requires use of a low iodine diet (< or = 50 micrograms iodine per day) to enhance the delivery of I-131 to thyroid remnants or carcinoma. Because there are no commercial low-iodine tube-feeding diets, the authors formulated and tested a suitable diet that is appropriate for home preparation using commonly available ingredients. A patient was placed on this diet in anticipation of radioiodine therapy after surgical resection of a thyroid carcinoma recurrence in his neck. This patient reduced his 24-hour urinary iodine excretion from 378 micrograms iodine to 13 micrograms iodine after 15 days on the diet. Analysis of the diet reveals that it is nutritionally complete and delivers only 18.2 micrograms of iodine for each 1000 kcal. This diet should improve I-131 therapy of differentiated thyroid carcinoma in patients requiring tube feedings.

Studies on the incorporation of sn-[1,3-14C]glycerol 3-phosphate into glycerolipids by intestinal mucosa.

Intestinal mucosal microsomes from several animal species (non-fasted) were used to study the formation of glycerolipids from sn-[1,3-14C]glycerol 3-phosphate and palmitoyl-CoA. Rates of glycerolipid biosynthesis were species dependent, since mouse and rat were quite low compared to hamster, guinea pig and man. Under the usual incubation conditions, guinea pig intestinal microsomes formed primarily phosphatidic acid (85-90%). However, when Mg2+ was added to incubations containing intestinal microsomes prepared in the presence of 5 mM EDTA, there was a marked increase in neutral lipid biosynthesis (5-10-fold). These results suggest that intestinal microsomes contain mg2+-dependent phosphatidate phosphohydrolase (EC 3.1.3.4) which is involved in glycerolipid biosynthesis. All divalent cations studied increased sn-glycerol-3-phosphate acyltransferase (EC 2.3.1.15) activity; however, Ca2+, Ba2+, Zn2+, Cd2+, Ni2+, and Mn2+ antagonized the Mg2+-dependent rise in neutral lipid formation. In all cellular preparations studied, the ratio of neutral lipid (diacylglycerol + triacylglycerol) to total lipid (phosphatic acid + neutral lipid) was low, suggesting that phosphatidate phosphohydrolase may be rate limiting in intestinal neutral glycerolipid biosynthesis.