Pollinator population size and pollination ecosystem service responses to enhancing floral and nesting resources

Modeling pollination ecosystem services requires a spatially explicit, process‐based approach because they depend on both the behavioral responses of pollinators to the amount and spatial arrangement of habitat and on the within‐ and between‐season dynamics of pollinator populations in response to land use. We describe a novel pollinator model predicting flower visitation rates by wild central‐place foragers (e.g., nesting bees) in spatially explicit landscapes. The model goes beyond existing approaches by: (1) integrating preferential use of more rewarding floral and nesting resources; (2) considering population growth over time; (3) allowing different dispersal distances for workers and reproductives; (4) providing visitation rates for use in crop pollination models. We use the model to estimate the effect of establishing grassy field margins offering nesting resources and a low quantity of flower resources, and/or late‐flowering flower strips offering no nesting resources but abundant flowers, on bumble bee populations and visitation rates to flowers in landscapes that differ in amounts of linear seminatural habitats and early mass‐flowering crops. Flower strips were three times more effective in increasing pollinator populations and visitation rates than field margins, and this effect increased over time. Late‐blooming flower strips increased early‐season visitation rates, but decreased visitation rates in other late‐season flowers. Increases in population size over time in response to flower strips and amounts of linear seminatural habitats reduced this apparent competition for pollinators. Our spatially explicit, process‐based model generates emergent patterns reflecting empirical observations, such that adding flower resources may have contrasting short‐ and long‐term effects due to apparent competition for pollinators and pollinator population size increase. It allows exploring these effects and comparing effect sizes in ways not possible with other existing models. Future applications include species comparisons, analysis of the sensitivity of predictions to life‐history traits, as well as large‐scale management intervention and policy assessment.     

Uracil-DNA glycosylase in base excision repair and adaptive immunity: species differences between man and mouse

Genomic uracil is a DNA lesion but also an essential key intermediate in adaptive immunity. In B cells, activation-induced cytidine deaminase deaminates cytosine to uracil (U:G mispairs) in Ig genes to initiate antibody maturation. Uracil-DNA glycosylases (UDGs) such as uracil N-glycosylase (UNG), single strand-selective monofunctional uracil-DNA glycosylase 1 (SMUG1), and thymine-DNA glycosylase remove uracil from DNA. Gene-targeted mouse models are extensively used to investigate the role of these enzymes in DNA repair and Ig diversification. However, possible species differences in uracil processing in humans and mice are yet not established. To address this, we analyzed UDG activities and quantities in human and mouse cell lines and in splenic B cells from Ung(+/+) and Ung(-/-) backcrossed mice. Interestingly, human cells displayed ～15-fold higher total uracil excision capacity due to higher levels of UNG. In contrast, SMUG1 activity was ～8-fold higher in mouse cells, constituting ～50% of the total U:G excision activity compared with less than 1% in human cells. In activated B cells, both UNG and SMUG1 activities were at levels comparable with those measured for mouse cell lines. Moreover, SMUG1 activity per cell was not down-regulated after activation. We therefore suggest that SMUG1 may work as a weak backup activity for UNG2 during class switch recombination in Ung(-/-) mice. Our results reveal significant species differences in genomic uracil processing. These findings should be taken into account when mouse models are used in studies of uracil DNA repair and adaptive immunity.     

Resonance Raman spectroscopy of ribonucleotide reductase. Evidence for a deprotonated tyrosyl radical and photochemistry of the binuclear iron center

Native ribonucleotide reductase from Escherichia coli exhibits a resonance-enhanced Raman mode at 1498 cm-1 that is characteristic of a tyrosyl radical. The Raman frequency as well as the absorption maximum at 410 nm identifies the radical as being in a deprotonated state. The B2 subunit of ribonucleotide reductase shows an additional resonance Raman mode at 493 cm-1 that has been assigned to the symmetric stretch of an Fe-O-Fe moiety. When samples of active B2 or metB2 are exposed to a tightly focused laser beam at 406.7 nm, there is a loss of intensity at 493 cm-1 and the appearance of a new peak at 595 cm-1. Although the 595-cm-1 feature was previously assigned to an Fe-OH vibration on the basis of its 23-cm-1 shift to lower energy in H2(18)O and the apparent dependence of its intensity on pH [Sj?berg, B. M., Loehr, T. M., & Sanders-Loehr, J. (1987) Biochemistry 26, 4242], the present studies indicate that the intensity of this mode is dependent primarily on input laser power. The peak at 595 cm-1 is more plausibly assigned to a new vs(Fe-O-Fe) mode in view of its lack of the deuterium isotope dependence expected for an Fe-OH mode and its resonant scattering cross section which is comparable to that of the 493-cm-1 mode. This new species has a calculated Fe-O-Fe angle of approximately 113 degrees compared to approximately 138 degrees calculated for the Fe-O-Fe unit in unmodified protein B2. One possible explanation for the photoinduced vibrational mode is that a bridging solvent molecule has been inserted in place of a bridging carboxylate.     

Inhibition and promotion of cholesterol crystallization by protein fractions from normal human gallbladder bile

Pooled, normal human gallbladder biles were initially separated on a molecular sieving chromatography column to remove soluble mucin glycoproteins as well as high molecular weight proteins (greater than 200,000). The remaining lower molecular weight proteins and other bile components were then examined by lectin affinity chromatography with four different types of lectin. The separated bound fractions were compared for inhibiting and promoting activities with a newly devised sensitive cholesterol crystal growth assay and for differences in electrophoretic patterns on SDS-gels. Protein factors (presumably glycoproteins) were found to have both inhibiting and promoting activities, even in the absence of cholesterol gallstone disease. The promoting effect was indicated by shortened crystal detection times and increases in crystal growth rate; whereas the inhibiting effect was indicated by decreases in crystal growth rate and reductions in the final crystal concentration as determined by the growth assay. Affinity chromatography mitigated the major problems of removing both lipids and pigment from the glycoproteins. In addition, partial purification of bound fractions with potent cholesterol crystal nucleation-altering activity can be obtained by this technique.     

Magnetic interaction between the tyrosyl free radical and the antiferromagnetically coupled iron center in ribonucleotide reductase

Ribonucleotide reductases from Escherichia coli and from mammalian cells are heterodimeric enzymes. One of the subunits, in the bacterial enzyme protein B2 and in the mammalian enzyme protein M2, contains iron and a tyrosyl free radical that both are essential for enzyme activity. The iron center in protein B2 is an antiferromagnetically coupled pair of high-spin ferric ions. This study concerns magnetic interaction between the tyrosyl radical and the iron center in the two proteins. Studies of the temperature dependence of electron paramagnetic resonance (EPR) relaxation and line shape reveal significant differences between the free radicals in proteins B2 and M2. The observed temperature-dependent enhanced EPR relaxation and line broadening of the enzyme radicals are furthermore completely different from those of a model UV-induced free radical in tyrosine. The results are discussed in terms of magnetic dipolar as well as exchange interactions between the free radical and the iron center in both proteins. The free radical and the iron center are thus close enough in space to exhibit magnetic interaction. For protein M2 the effects are more pronounced than for protein B2, indicating a stronger magnetic interaction.     

Glucose formation in human skeletal muscle. Influence of glycogen content.

Eight men exercised at 66% of their maximal isometric force to fatigue after prior decrease in the glycogen store in one leg (low-glycogen, LG). The exercise was repeated with the contralateral leg (control) at the same relative intensity and for the same duration. Muscle (quadriceps femoris) glycogen content decreased in the LG leg from 199 +/- 17 (mean +/- S.E.M.) to 163 +/- 16 mmol of glucosyl units/kg dry wt. (P less than 0.05), and in the control leg from 311 +/- 23 to 270 +/- 18 mmol/kg (P less than 0.05). The decrease in glycogen corresponded to a similar accumulation of glycolytic intermediates. Muscle glucose increased in the LG leg during the contraction, from 1.8 +/- 0.1 to 4.3 +/- 0.6 mmol/kg dry wt. (P less than 0.01), whereas no significant increase occurred in the control leg (P greater than 0.05). It is concluded that during exercise glucose is formed from glycogen through the debranching enzyme when muscle glycogen is decreased to values below about 200 mmol/kg dry wt.     

Compounds with capacity to quench the tyrosyl radical in Pseudomonas aeruginosa ribonucleotide reductase

JBIC Journal of Biological Inorganic Chemistry - Ribonucleotide reductase (RNR) has been extensively probed as a target enzyme in the search for selective antibiotics. Here we report on the...