Plant fructans stabilize phosphatidylcholine liposomes during freeze-drying.

Fructans have been implicated as protective agents in the drought and freezing tolerance of many plant species. A direct proof of their ability to stabilize biological structures under stress conditions, however, is still lacking. Here we show that inulins (linear fructose polymers) isolated from chicory roots and dahlia tubers stabilize egg phosphatidylcholine large unilamellar vesicles during freeze-drying, while another polysaccharide, hydroxyethyl starch, was completely ineffective. Liposome stability was assessed after rehydration by measuring retention of the soluble fluorescent dye carboxyfluorescein and bilayer fusion. Inulin was an especially effective stabilizer in combination with glucose. Analysis by HPLC showed that the commercial inulin preparations used in our study contained no low molecular mass sugars that could be responsible for the observed stabilizing effect of the fructans. Fourier transform infrared spectroscopy showed a reduction of the gel to liquid-crystalline phase transition temperature of dry egg PtdCho by more than 20 degrees C in the presence of inulin. A direct interaction of inulin with the phospholipid in the dry state was also indicated by dramatic differences in the phosphate asymmetric stretch region of the infrared spectrum between samples with and without the polysaccharide.     

Current and emerging commercial optical biosensors.

The field of commercial optical biosensors is rapidly evolving, with new systems and detection methods being developed each year. This review outlines the currently available biosensor hardware and highlights unique features of each platform. Affinity-based biosensor technology, with its high sensitivity, wide versatility and high throughput, is playing a significant role in basic research, pharmaceutical development, and the food and environmental sciences. Likewise, the increasing popularity of biosensors is prompting manufacturers to develop new instrumentation for dedicated applications. We provide a preview of some of the emerging commercial systems that are dedicated to drug discovery, proteomics, clinical diagnostics and routine biomolecular interaction analysis.     

De novo-synthesized ceramide signals apoptosis in astrocytes via extracellular signal-regulated kinase.

Recent observations support the importance of ceramide synthesis de novo in the induction of apoptosis. However, the downstream targets of de novo-synthesized ceramide are unknown. Here we show that palmitate incorporated into ceramide and induced apoptotic DNA fragmentation in astrocytes. These effects of palmitate were exacerbated when fatty acid breakdown was uncoupled and were not evident in neurons, which show a very low capacity to take up and metabolize palmitate. Palmitate-induced apoptosis of astrocytes was prevented by L-cycloserine and fumonisin B1, two inhibitors of ceramide synthesis de novo, and by PD098059, an inhibitor of the extracellular signal-regulated kinase (ERK) cascade. Accordingly, palmitate activated ERK by a process that was dependent on ceramide synthesis de novo and Raf-1, but independent of kinase suppressor of Ras. Other potential targets of ceramide in the control of cell fate, namely, c-Jun amino-terminal kinase, p38 mitogen-activated protein kinase, and protein kinase B, were not significantly affected in astrocytes exposed to palmitate. Results show that the Raf-1/ERK cascade is the selective downstream target of de novo-synthesized ceramide in the induction of apoptosis in astrocytes and also highlight the importance of ceramide synthesis de novo in apoptosis of astrocytes, which might have pathophysiological relevance.     

Synthesis and characterisation of ferrocene-containing β-diketonato complexes of rhodium(I) and rhodium(III)

The synthesis of new β-diketonato rhodium(I) complexes of the type [Rh(FcCOCHCOR)(CO)₂] and [Rh(FcCOCHCOR)(CO)(PPh₃)] with Fc=ferrocenyl and R=Fc, C₆H₅, CH₃ and CF₃ are described. ¹H, ¹³C and ³¹P NMR data showed that for each of the non-symmetric β-diketonato mono-carbonyl rhodium(I) complexes, two isomers exist in solution. The equilibrium constant, K_c, which relates these two isomers in an equilibrium reaction, are concentration independent but temperature and solvent dependent. Δ_rG, Δ_rH and Δ_rS values for this equilibrium have been determined and a linear relationship between solvent polarity on the Dimroth scale and K_c exists. The relationship between RhP bond lengths, d(RhP), and ³¹P NMR peak positions as well as coupling constants ¹J(³¹P¹⁰³Rh) has been quantified to allow calculation of approximate d(RhP) values. Variations in d(RhP) for [Rh(RCOCHCOR′)(CO)(PPh₃)] complexes have also been related to the group electronegativities (Gordy scale) of the terminal β-diketonato R groups trans to PPh₃. A measure of the electron density on the rhodium centre of [Rh(RCOCHCOR′)(CO)(PPh₃)] may be expressed in terms of the IR carbonyl stretching wave number, ν(CO), the sum of the group electronegativities of the R and R′ groups, (χ_R+χ_R′), or the observed pK_a^′ values of the free β-diketones RCOCH₂COR^′. An empirical relationship between ν(CO) and either pK_a^′ or (χ_R+χ_R′) has also been quantified.     

Role of kallikrein-kininogen system in insulin-stimulated glucose transport after muscle contractions.

Serum proteins [molecular weight (MW) > 10,000] are essential for increased insulin-stimulated glucose transport after in vitro muscle contractions. We investigated the role of the kallikrein-kininogen system, including bradykinin, which is derived from kallikrein (MW > 10,000)-catalyzed degradation of serum protein kininogen (MW > 10,000), on this contraction effect. In vitro electrical stimulation of rat epitrochlearis muscles was performed in 1) rat serum +/- kallikrein inhibitors; 2) human plasma (normal or kallikrein-deficient); 3) rat serum +/- bradykinin receptor-2 inhibitors; or 4) serum-free buffer +/- bradykinin. 3-O-methylglucose transport (3-MGT) was measured 3.5 h later. Serum +/- kallikrein inhibitors tended (P = 0.08) to diminish postcontraction insulin-stimulated 3-MGT. Contractions in normal plasma enhanced insulin-stimulated 3-MGT vs. controls, but contractions in kallikrein-deficient plasma did not. Supplementing rat serum with bradykinin receptor antagonist HOE-140 during contraction did not alter insulin-stimulated 3-MGT. Muscles stimulated to contract in serum-free buffer plus bradykinin did not have enhanced insulin-stimulated 3-MGT. Bradykinin was insufficient for postcontraction-enhanced insulin sensitivity. However, results with kallikrein inhibitors and kallikrein-deficient plasma suggest kallikrein plays a role in this improved insulin action.     

Photosynthesis in an invasive grass and native forb at elevated CO2 during an El Niño year in the Mojave Desert

Annual and short-lived perennial plant performance during wet years is important for long-term persistence in the Mojave Desert. Additionally, the effects of elevated CO₂ on desert plants may be relatively greater during years of high resource availability compared to dry years. Therefore, during an El Niño year at the Nevada Desert FACE Facility (a whole-ecosystem CO₂ manipulation), we characterized photosynthetic investment (by assimilation rate-internal CO₂ concentration relationships) and evaluated the seasonal pattern of net photosynthesis (A_net) and stomatal conductance (g_s) for an invasive annual grass, Bromus madritensis ssp. rubens and a native herbaceous perennial, Eriogonum inflatum. Prior to and following flowering, Bromus showed consistent increases in both the maximum rate of carboxylation by Rubisco (V_Cmax) and the light-saturated rate of electron flow (J_max) at elevated CO₂. This resulted in greater A_net at elevated CO₂ throughout most of the life cycle and a decrease in the seasonal decline of maximum midday A_net upon flowering as compared to ambient CO₂. Eriogonum showed significant photosynthetic down-regulation to elevated CO₂ late in the season, but the overall pattern of maximum midday A_net was not altered with respect to phenology. For Eriogonum, this resulted in similar levels of A_net on a leaf area basis as the season progressed between CO₂ treatments, but greater photosynthetic activity over a typical diurnal period. While g_s did not consistently vary with CO₂ in Bromus, it did decrease in Eriogonum at elevated CO₂ throughout much of the season. Since the biomass of both plants increased significantly at elevated CO₂, these patterns of gas exchange highlight the differential mechanisms for increased plant growth. The species-specific interaction between CO₂ and phenology in different growth forms suggests that important plant strategies may be altered by elevated CO₂ in natural settings. These results indicate the importance of evaluating the effects of elevated CO₂ at all life cycle stages to better understand the effects of elevated CO₂ on whole-plant performance in natural ecosystems.     

The effects of concentrate energy source on feed intake and rumen fermentation parameters of dairy cows offered a range of grass silages

The effects of concentrate energy source on feed intake and rumen fermentation parameters of lactating dairy cattle, offered one of three grass silages differing in fermentation and intake characteristics, were evaluated in a partially balanced changeover design experiment involving four rumen fistulated dairy cows. Three silages were harvested using different management practices prior to and at ensiling. Silages A and C and silage B were harvested from primary or secondary regrowths either untreated or treated with a bacterial inoculant. For silages A, B and C, dry matter (DM) concentrations were 334, 197 and 183 g/kg (S.E. 3.1), pH values 4.00, 4.79 and 4.80 (S.E. 0.042) and ammonia nitrogen (N) concentrations were 123, 319 and 295 g/kg total N (S.E. 20.0), respectively. Two concentrates were formulated to contain similar crude protein, effective rumen degradable protein, digestible undegradable protein and metabolisable energy concentrations but using different carbohydrate sources to achieve a wide range of starch concentrations. For the low and high starch concentrates starch concentrations were 17 and 304 g/kg DM and acid detergent fibre concentrations were 170 and 80 g/kg DM, respectively. The silages were offered ad libitum, supplemented with 10 kg fresh concentrate daily. For silages A, B and C, DM intakes were 10.9, 7.2 and 8.6 kg/day and concentrate energy sources did not alter (P>0.05) intake. Increasing the level of starch in the concentrate decreased the molar concentration of acetate (P<0.05) and tended to increase the molar concentration of propionate (P<0.1). Silage type altered the molar concentration of acetate (P<0.01) and the acetate:propionate ratio (P<0.05). There were no silagetype×concentrate interactions (P>0.05) on silage intake or rumen fermentation parameters. It is concluded that when concentrate and silage form equal proportions of the diet, the composition of the silage has an over-riding influence on rumen fermentation parameters. Furthermore, the changes in milk fat concentration, observed in a concurrent production study, due to changes in silage and concentrate types can be accounted for by changes in the ratio of lipogenic to glucogenic precursors in the rumen fluid.