Urinary excretion of mercury, copper and zinc in subjects exposed to mercury vapour

The excretion of mercury, copper and zinc in urine, and mercury in whole blood andplasma, was determined in 40 chloralkali workers exposed to mercury vapour and 40age-matched referents. The Hg concentrations in whole blood, plasma and urine werehigher in the exposed group (35 nmol l, 30 nmol l,and 11.5 nmol mmol creatinine, respectively) in comparison with thereference group (15 nmol l, 6.3 nmol l, and 1.8nmol mmol creatinine, respectively). The urinary copper excretionwas similar in the two groups, while U-Zn excretion was significantly higher (P = 0.04)in the exposed group, median 0.83 mmol mmol creatinine versus 0.76mnmol mmol creatinine in the reference group. In a subgroup of exposedworkers with current U-Hg above 11.5 nmol lmmolcreatinine (20 mg g creatinine) the medianU-Zn was 1.1 mmol mmol creatinine. In both groups smokers had highU-Zn levels than non smokers. When both U-Hg and smoking were taken into account in alinear regression model, there was a significant association between U-Hg and U-Zn inthe combined group of exposed and referents (P = 0.002). This study indicates thatmercury exposure in humans, as in animals, causes increased urinary excretion of zinc.The mechanisms may be induced synthesis of metallothionein in the kidneys, displacementof Zn from preexisting metallothionein by Hg, or a decreased reabsorption of zinc in thekidneys owing to a slight tubular dysfunction.     

Characterization of the high affinity heparin binding site of the Alzheimer's disease βA4 amyloid precursor protein (APP) and its enhancement by zinc(II)

The Alzheimer's disease βA4 amyloid precursor protein (APP) has been shown to be involved in a diverse set of biological protein precursor-like proteins (APLP1 and APLP2) belong to a superfamily of proteins that are probably functionally related. In order to characterize the cell adhesion properties of APP the brain specific isoform APP₆₉₅ was purified and used to assess the binding to herparin, a structural and functional analogue of the glycosaminoglycan heparan sulfate. We show that APP binds in a time dependent and saturable manner to heparin. The salt concentration of 620 mM at which APP elutes from heparin Sepharose is greater than physiological. Tha apparent equilibrium constant for dissociation was determined to be 300 pM for APP binding to heparin Sepharose. A high affinity heparin binding site was identified within a region conversed in rodent and human APP, APLP1 and APLP2. This binding site was located between residues 316-337 of APP₆₉₅ which is within the carbohydrate domain of APP. We also demonstrate an interaction between this heparin binding site and the zinc(II) binding site which is conserved in all members of the APP superfamily. We show by using an automated surface plasmon resonance biosensor (BIAcore, Pharmacia) that the affinity for heparin is increased two- to four-fold in the presence of micromolar zinc(II). The identification of zinc-enhanced binding of APP to heparin sulfate side chains of proteoglycans offers a molecular link between zinc(II), as a putative environmental toxin for Alzheimer's disease, and aggregation of amyloid βA4 protein.     

Avian feather development: relationships between morphogenesis and keratinization

Morphogenesis and expression of the alpha and beta keratin polypeptides are controlled by epidermal-dermal interactions during development of avian skin derivatives. We have examined the relationship between morphogenesis of the embryonic feather and expression of the feather alpha and beta keratins by routine histology, indirect-immunofluorescence, and SDS-PAGE. Initially beta keratins are expressed only in the feather sheath. Following barb ridge morphogenesis beta keratins can be detected in the barb ridge, coincident with the differentiation of barb ridge cells into eight distinct morphological types. Beta keratinization occurs in gradients; from feather apex to base, and from periphery of the barb ridge to the interior. The onset of beta keratinization in the barb ridges is paralleled by an increase in the major feather beta keratin polypeptides, as detected by SDS-PAGE. The alpha keratins are present in both the periderm and feather sheath at early stages of feather development, but become greatly reduced after hatching, when the down feather emerges from the sheath.     

Effect of temperature on nuclear membranes and nucleo-cytoplasmic RNA-transport in Tetrahymena grown at different temperatures.

The effect of temperature on the nuclear envelope structure and the transport of total RNA and ribosomal subunits from nucleus to cytoplasm was examined in Tetrahymena cells propagated at two different temperatures. Freeze-etch electron microscopy of cells grown at 23 and 18 degrees C detects the emergence of smooth areas on the fracture faces of the nuclear membranes upon lowering the temperature below approximately 15 and approximately 12 degrees C, respectively. Coincident with these freeze-etch changes, a discontinuous decrease is observed in the nucleocytoplasmic RNA-transport; this is probably not due to a cease in RNA-synthesis. Below the thermotropic discontinuity observed in the transport of total RNA in 18 degrees-cells the nucleocytoplasmic transport of the small and large ribosomal subunits is equally retarded. Recent temperature studies on the endoplasmic reticulum membranes of Tetrahymena suggest that the freeze-etch changes in the nuclear membranes are induced by a thermotropic clustering of the membrane lipids. We conclude that this lipid clustering induces the permanent protein constituents in the nuclear envelope pore complexes to change from a relatively "open" into a relatively "closed" state thus causing the observed decrease in RNA-transport.     

Molecular genetics of mutants of Rhizobium leguminosarum which fail to fix nitrogen

Summary Mutants of Rhizobium leguminosarum which failed to fix nitrogen within nodules on peas were isolated following the insertion of the transposon Tn5 into pRL1JI, a Rhizobium plasmid known to carry the genes for nitrogenase. The sites of the Tn5 insertions were identified by restriction endonuclease mapping of cloned fragments of DNA from the mutant strains. One group of mutants was located within 4 kilobases of the structural genes for nitrogenase and another was located about 30 kilobases from this region. Two mutants from the first group, one of which appeared to be affected in a nitrogenase gene, induced nodules that contained bacterioids, but the number of plant cells containing bacteroids was less than in a normal nodule. Another group of mutants, which was located about 30 kilobases from the nitrogenase genes failed to form bacterioids. Electron microscopy of the nodules induced by these mutants indicated that there was a defect in their release from infection threads.     

Broadly reactive murine cytotoxic cells induced in vitro under syngeneic conditions

Mouse spleen cells became cytotoxic in short-term 51Cr-release assays for a wide variety of target cells after 5 days of culture in vitro with polyinosinic acid in a system that was otherwise entirely syngeneic. This study characterizes these effector cells with respect to target specificity, effect of donor age, time course of their appearance, mouse strain differences, and expression of differentiation antigens Thy-1, Lyt-1, Lyt-2, NK-1, and asialo GM1. The combination of properties of this cytotoxic cell response that make it unique are that a) the broadly reactive cytotoxic activity developed from unprimed spleen cells in the absence of either foreign cells or foreign serum; b) the response did not peak until 4 to 5 days of culture in vitro; c) the broad reactivity pattern included freshly dispersed primary syngeneic sarcoma cells and cultured syngeneic fibroblasts but did not include syngeneic lymphoblast target cells; d) the response was largely monoclonal as defined by target cell binding; and e) cytotoxic cell activity was sensitive in complement-mediated treatments to both anti-NK and anti-theta but not to anti-Lyt-2, anti-Lyt-1, or anti-asialo GM1. Both high- and low-responding mouse strains have been identified.     

Proteins of bovine leudemia virus: p. 15 is the major phosphorprotein.

Sodium dodecylsulfate-polyacrylamide gel electrophoresis of bovine leukemia virus (BLV) grown in fetal lamb kidney cells in the presence of 32P-phosphoric acid showed that the slightly basic 15000 D protein (pp 15) is the major phosphorylated component of the virus. This result further distinguishes BLV from mammalian type C viruses which possess acidic major phosphorproteins.     

Assignment of proximal histidyl imidazole exchangeable proton NMR resonances to individual subunits in hemoglobins A,Boston, Iwate and Milwaukee

The proton nmr spectra of the synthetic valency hybrids, α₂(β⁺CN)₂, (α⁺CN)₂β₂ of hemoglobin A and the natural valency hybrids of the mutant hemoglobins Boston, Iwate and Milwaukee have led to the unambiguous assignment of the two proximal histidyl imidazole exchangeable proton signals at 64 and 76 ppm to individual α and β subunits, respectively. New single non-exchangeable proton resonances detected in the extreme downfield region of the spectra of Hbs Boston and Iwate are tentatively assigned to the coordinated tyrosine of the mutated α chains.     

Demonstration of RNA-dependent DNA polymerase activity in non-disrupted type D-retravirus particles after treatment with EDTA.

The type D-retraviruses PMF virus (PMFV) and Mason-Pfizer moneky virus (MPMV) show RNA-dependent DNA polymerase (revertase) activity after treatment of the nondisrupted virions with the chelating agent ethylenediaminetetraacetate (EDTA). In the range of 1 to 5 mM, the effect is dependent on the concentration of EDTA. As compared with Nonidet P40 disrupted particles treatment of PMFV with EDTA results in a revertase activity of about 65%. Simultaneous addition of Mg- or Ca-ions prevents the EDTA effect. Other divalent cation-binding agents (o-phenathroline, thiosemicarbazide) do not induce an EDTA-like effect. It is suggested that EDTA chelates divalent ions responsible for the structural organization of the viral membrane which, after chelation, gets permeable for the exogenous revertase template.