Changes in drinking water selenium and mortality for coronary disease in a residential cohort

In a part of the municipal territory of Reggio Emilia, northern Italy, selenium in drinking water decreased from 7 μg/L to less than 1 μg/L. In a cohort of 4419 individuals, previously exposed for at least 5 yr to the drinking water with higher selenium content, the 7-yr temporal distribution of deaths for coronary disease and for stroke was analyzed to examine a possible relationship with changes in drinking water selenium. From January 1986 until August 1988, when tap water selenium was 7 μg/L, deaths for coronary disease were one in males and two in females. After the decrease in drinking water selenium, 21 and 10 coronary deaths were observed, respectively, in males and in females from September 1988 to December 1992. No significant difference in the temporal distribution of stroke deaths was observed both in males and in females. Even if an effect of chance and aging in the temporal distribution of coronary deaths may not be excluded, findings of the study seem to be consistent with the hypothesis of a beneficial effect of selenium on coronary disease mortality.     

Side reactions in the synthesis of phosphotyrosine-containing peptides

Summary A series of phosphopeptides Tyr(PO₃H₂)-Val-Pro-Xxx-Leu (Xxx=Met, Met(O), Nle, Dab or Cys), derived from the native platelet-derived growth factor- receptor (PDGF-) sequence, has been prepared to study their interaction with the src-homology 2 (SH2) domains of the p85 subunit of PI3 kinase. The phosphopeptides were synthesized using Fmoc methodology incorporating N-Boc dibenzyl-protected phosphotyrosine (Boc-Tyr[PO₃(Bzl)₂]) as the N-terminal amino acid, since the benzyl groups can be removed during resin cleavage with TFA. Only peptides containing methionine were found to exist partially as S-benzyl sulfonium salts after TFA cleavage from the resin. The desired peptide could be obtained from the S-benzyl sulfonium salt by hydrogenolysis.     

The human glucagon receptor encoding gene: structure, cDNA sequence and chromosomal localization

Characterization of the human glucagon-receptor-encoding gene (GGR) should provide a greater understanding of blood glucose regulation and may reveal a genetic basis for the pathogenesis of diabetes. A cDNA encoding a complete functional human glucagon receptor (GGR) was isolated from a liver cDNA library by a combination of polymerase chain reaction and colony hybridization. The cDNA encodes a receptor protein with 80% identity to rat GGR that binds [¹²⁵I] glucagon and transduces a signal leading to increases in the concentration of intracellular cyclic adenosine 3′,5′-monophosphate. Southern blot analysis of human DNA reveals a hybridization pattern consistent with a single GGR locus. In situ hybridization to metaphase chromosome preparations maps the GGR locus to chromosome 17q25. Analysis of the genomic sequence shows that the coding region spans over 5.5 kb and is interrupted by 12 introns.     

A novel isotope labeling protocol for bacterially expressed proteins

Summary A novel protocol for isotopically labeling bacterially expressed proteins is presented. This method circumvents problems related to poor cell growth, commonly associated with the use of minimal labeled media, and problems with protein induction encountered, less commonly, when using enriched labeled media. The method involves initially growing the bacterial cells to high optical density in a commercially available enriched labeled medium. Following a suitable growth period, the cells are transferred to a different (minimal) labeled medium, appropriate for induction. The method is demonstrated using the protein melanoma growth stimulating activity (MGSA).     

Round-cell mutants of Salmonella typhimurium produced by transposition mutagenesis: Lethality of rodA and mre mutations

Summary Thirty-three insertions of transposon Tn10l6l7 into genes involved in the control of rod cell shape were isolated in Salmonella typhimurium by the characteristic glossy appearance of colonies composed of spherical cells. Genetic tests demonstrated that 25 (76%) were insertions in the rodA gene, 7 (21 %) were mre mutants, and 1 (3%) was a divD mutant. No insertion in the pbpA gene were found. Insertions in cell shape genes only appeared when strains displaying resistance to mecillinam (not caused by -lactamase production) were employed. Neither rodA nor mre insertions could be transduced to wild-type strains but they were normally accepted by mecillinam-resistant derivatives and by cya and crp mutants, which, unlike the corresponding Escherichia coli strains, did not display resistance to mecillinam. On the other hand, the divD insertion could be efficiently transduced to any strain. It is concluded that the rodA, mre, and divD genes are involved in the control of rod cell shape but, in addition, the RodA and Mre products perform some function(s) that is essential for wild-type cells but dispensable for some mecillinam-resistant strains, and for cya and crp mutants.     

Elevated CO2 and drought alter tissue water relations of birch (Betula populifolia Marsh.) seedlings

The effect of increasing atmospheric CO₂ concentrations on tissue water relations was examined in Betula populifolia, a common pioneer tree species of the northeastern U.S. deciduous forests. Components of tissue water relations were estimated from pressure volume curves of tree seedlings grown in either ambient (350 l l^–1) or elevated CO₂ (700 l l^–1), and both mesic and xeric water regimes. Both CO₂ and water treatment had significant effects on osmotic potential at full hydration, apoplasmic fractions, and tissue elastic moduli. Under xeric conditions and ambient CO₂ concentrations, plants showed a decrease in osmotic potentials of 0.15 MPa and an increase in tissue elastic moduli at full hydration of 1.5 MPa. The decrease in elasticity may enable plants to improve the soil-plant water potential gradient given a small change in water content, while lower osmotic potentials shift the zero turgor loss point to lower water potentials. Under elevated CO₂, plants in xeric conditions had osmotic potentials 0.2 MPa lower than mesic plants and decreased elastic moduli at full hydration. The increase in tissue elasticity at elevated CO₂ enabled the xeric plants to maintain positive turgor pressures at lower water potentials and tissue water contents. Surprisingly, the elevated CO₂ plants under mesic conditions had the most inelastic tissues. We propose that this inelasticity may enable plants to generate a favorable water potential gradient from the soil to the plant despite the low stomatal conductances observed under elevated CO₂ conditions.     

CO2-induced growth enhancements of co-occurring tree species decline at different rates

To elucidate how enriched CO₂ atmospheres, soil fertility, and light availability interact to influence the long-term growth of tree seedlings, six co-occurring members of temperate forest communities including ash (Fraxinus americana L.), gray birch (Betula populifolia), red maple (Acer rubrum), yellow birch (Betula alleghaniensis), striped maple (Acer pensylvanicum), and red oak (Quercus rubra L.) were raised in a glasshouse for three years in a complete factorial design. After three years of growth, plants growing in elevated CO₂ atmospheres were generally larger than those in ambient CO₂ atmospheres, however, magnitudes of CO₂-induced growth enhancements were contingent on the availability of nitrogen and light, as well as species identity. For all species, magnitudes of CO₂-induced growth enhancements after one year of growth were greater than after three years of growth, though species' growth enhancements over the three years declined at different rates. These results suggest that CO₂-induced enhancements in forest productivity may not be sustained for long periods of time. Additionally, species' differential growth responses to elevated CO₂ may indirectly influence forest productivity via long-term species compositional changes in forests.     

Interactions between nitrate and ammonium during uptake by carob seedlings and the effect of the form of earlier nitrogen nutrition

Seedlings of carob ( Ceratonia siliqua L. cv. Mulata) were used in two sets of experiments in order to evaluate; (1) the reciprocal effects of each nitrogen form on net uptake of nitrate and ammonium, and (2) the effect of earlier nitrogen nutrition on ammonium versus nitrate uptake. In the former group of experiments we studied the kinetics of nitrate and ammonium uptake as well as the interference of each of the two forms with net uptake of ammonium and nitrate by both nitrogen depleted and nitrogen fed carob seedlings. On the whole, nitrogen depletion led to increase in both affinity and V_max of the system for both forms of nitrogen, at the same time as the effects of nitrate on uptake of ammonium and vice versa were concentration dependent. In the second group of experiments the effects of earlier nitrogen nutrition on nitrate and ammonium uptake were characterized, and in this case we observed that: (a) if only one form of N was supplied, ammonium was taken up in greater amounts than nitrate; (b) the presence of ammonium enhanced nitrate uptake; (c) ammonium uptake was inhibited by nitrate; (d) there was a significant effect of the earlier nitrogen nutrition on the response of the plants to a different nitrogen source. The latter was evident mainly as regards ammonium uptake by plants grown in ammonium nitrate. The interactions between nitrate and ammonium uptake systems are discussed on the basis of the adaptation to the nitrogen source during early growth.     

Interpreting the role of phosphorus and growth rate in enhanced fungal induction of sesquiterpenes from Hyoscyamus muticus root cultures

The effect of thiamine limitation in combination with fungal elicitation on sesquiterpene (solavetivone) production was studied in Agrobacterium-transformed hairy-root cultures of Hyoscyamus muticus as a potential means of manipulating the growth rate independent of phosphorus availability. Limiting the initial supply of thiamine did not affect the growth of these cultures compared to growth at the control level of thiamine (0.01 g/l). There was also no enhancement in sesquiterpene production when thiamine supply was limited. Serial culturing in thiamine-free media suggests that these root cultures are not strictly auxotrophic for thiamine, in contrast to previously published results for untransformed root culture. The effect of phosphate limitation combined with elicitation on the production of solavetivone was examined at constant media volume to provide a constant elicitor concentration and to eliminate feedback-inhibition effects. Limiting the initial supply of phosphate to elicited cultures resulted in a twofold increase in solavetivone production as compared to the elicitation at control media phosphate levels (1.1mm). Because growth was attenuated, production per unit cell mass increased 11-fold compared to the control. The effect of phosphate limitation on solavetivone production at constant cell mass and elicitor per root mass was studied. Limiting the initial supply of phosphate to elicited cultures under these conditions did not result in enhanced production of solavetivone. The initially observed enhanced production of solavetivone at limiting initial phosphate concentrations is therefore due to factors other than the growth rate or phosphate involvement in secondary metabolism. Correspondence to: W. R. Curtis