Characterization of the metallocenter of rabbit skeletal muscle AMP deaminase. A new model for substrate interactions at a dinuclear cocatalytic Zn site

We have previously provided evidence for a dinuclear zinc site in rabbit skeletal muscle AMPD compatible with a (micro-aqua)(micro-carboxylato)dizinc(II) core with an average of two histidine residues at each metal site. XAS of the zinc binding site of the enzyme in the presence of PRN favors a model where PRN is added to the coordination sphere of one of the two zinc ions increasing its coordination number to five. The uncompetitive nature of the inhibition of AMPD by fluoride reveals that the anion probably displaces the nucleophile water molecule terminally coordinated to the catalytic Zn(1) ion at the enzyme C-terminus, following the binding of AMP at the Zn(2) ion located at N-terminus of the enzyme. Thus, the two Zn ions in the AMPD metallocenter operate together as a single catalytic unit, but have independent function, one of them (Zn(1)) acting to polarize the nucleophile water molecule, whilst the other (Zn(2)) acts transiently as a receptor for an activating substrate molecule. The addition of fluoride to AMPD also abolishes the cooperative behaviour induced in the enzyme by the inhibitory effect of ATP at acidic pH that probably resides in the competition with the substrate for an adenine nucleotide specific regulatory site located in the Zn(2) ion binding region and which is responsible for the positive homotropic cooperativity behaviour of AMPD.     

Design,Synthesis, Lipophilic Properties,and Binding Affinities of Potential Ligands in Positron Emission Tomography (PET) for Visualization of Brain Dopamine D4 Receptors

We report the synthesis of compounds structurally related to the high‐affinity dopamine D₄ receptor ligand N‐{2‐[4‐(3‐cyanopyridin‐2‐yl)piperazin‐1‐yl]ethyl}‐3‐methoxybenzamide ( 1e ). All compounds were specifically designed as potential PET radioligands for brain D₄ receptor visualization, having lipophilicity within a range for brain uptake and weak non‐specific binding (0.75<cLogP<3.15) and bearing a substituent for easy access to labeling with the positron emitter isotope ¹¹C or ¹⁸F. The best compound of the series, N‐{2‐[4‐(4‐chlorophenyl)piperazin‐1‐yl]ethyl}‐6‐fluoropyridine‐3‐carboxamide ( 7a ), displayed excellent selectivity over D₂ and D₃ receptors (>100‐fold), but its D₄ receptor affinity was suboptimal for imaging of brain D₄ receptors (K_i=30 nM ).     

Prey capture rates of two species of salmonids (Salmo trutta and Thymallus thymallus) in an artificial stream: effects of temperature on their functional response

The foraging success of predators depends on how their consumption of prey is affected by prey density under different environmental settings. Here, we measured prey capture rates of drift-feeding juvenile brown trout and European grayling at different prey densities in an artificial stream channel at 5 and 11?°C. Capture rates were lower at 5 than at 11?°C, and the difference was most pronounced at high prey densities. At high prey densities, we also observed that European grayling had higher capture rates than brown trout. Type III functional response curves, i.e. sigmoidal relationships between capture rates and prey densities, fitted the data better than type I (linear) and II (hyperbolic) curves for all four combinations of temperatures and species. These results may explain the dominance of grayling in stream habitats with low water velocities and results such as these may be of use when developing foraging-based food web models of lotic ecosystems that include drift-feeding salmonids.     

Synergistic effect of Aspergillus niger and Trichoderma reesei enzyme sets on the saccharification of wheat straw and sugarcane bagasse

Plant‐degrading enzymes can be produced by fungi on abundantly available low‐cost plant biomass. However, enzymes sets after growth on complex substrates need to be better understood, especially with emphasis on differences between fungal species and the influence of inhibitory compounds in plant substrates, such as monosaccharides. In this study, Aspergillus niger and Trichoderma reesei were evaluated for the production of enzyme sets after growth on two “second generation” substrates: wheat straw (WS) and sugarcane bagasse (SCB). A. niger and T. reesei produced different sets of (hemi‐)cellulolytic enzymes after growth on WS and SCB. This was reflected in an overall strong synergistic effect in releasing sugars during saccharification using A. niger and T. reesei enzyme sets. T. reesei produced less hydrolytic enzymes after growth on non‐washed SCB. The sensitivity to non‐washed plant substrates was not reduced by using CreA/Cre1 mutants of T. reesei and A. niger with a defective carbon catabolite repression. The importance of removing monosaccharides for producing enzymes was further underlined by the decrease in hydrolytic activities with increased glucose concentrations in WS media. This study showed the importance of removing monosaccharides from the enzyme production media and combining T. reesei and A. niger enzyme sets to improve plant biomass saccharification.     

Synthetic lactulose amines: novel class of anticancer agents that induce tumor-cell apoptosis and inhibit galectin-mediated homotypic cell aggregation and endothelial cell morphogenesis

Galectins, a family of structurally related carbohydrate-binding proteins, contribute to different events associated with cancer biology, including apoptosis, homotypic cell aggregation, angiogenesis and tumor-immune escape. To interfere with galectin-carbohydrate interactions during tumor progression, a current challenge is the design of specific galectin inhibitors for therapeutic purposes. Here, we report the synthesis of three novel low molecular weight synthetic lactulose amines (SLA): (1) N-lactulose-octamethylenediamine (LDO), (2) N,N'-dilactulose-octamethylenediamine (D-LDO), and (3) N,N'-dilactulose-dodecamethylenediamine (D-LDD). These compounds showed a differential ability to inhibit binding of galectin-1 and/or galectin-3 to the highly glycosylated protein 90K in solid-phase assays. In addition, each compound demonstrated selective regulatory effects in different events linked to tumor progression including tumor-cell apoptosis, homotypic cell aggregation, and endothelial cell morphogenesis. Our results suggest that galectin inhibitors with subtle differences in their carbohydrate structures may be potentially used to specifically block different steps of tumor growth and metastasis.     

An inexpensive instrument for sediment erosion-accumulation rate measurement in intertidal environments

A low-cost instrument to determine elevation changes in intertidal environments is presented. The instrument consists of two small PVC pipes driven into the soil and a ruler attached to a bar sustained by two rods that are inserted into the pipes during the measurement. This method cost only a fraction of similar ones described in the literature. Furthermore, because large numbers can be deployed in an area, statistically significant sedimentation-erosion rates can be obtained for places where spatial variances are very large.