Solid-Phase Synthesis of Biaryl Cyclic Peptides Containing a Histidine-Phenylalanine Linkage

The feasibility of the solid-phase intramolecular 4(5)-arylation of a histidine residue to obtain biaryl cyclic peptides bearing a His-Phe linkage was esta     

PHENOTYPIC PLASTICITY INDUCED IN TRANSPLANT EXPERIMENTS IN A MUTUALISTIC ASSOCIATION BETWEEN THE RED ALGA JANIA ADHAERENS (RHODOPHYTA,CORALLINALES) AND THE SPONGE HALICLONA CAERULEA (PORIFERA: HAPLOSCLERIDA): MORPHOLOGICAL RESPONSES OF THE ALGA1

The association between the red macroalga Jania adhaerens J. V. Lamour. and the sponge Haliclona caerulea is the most successful life‐form between 2 and 4 m depth in Mazatlán Bay (Mexican Pacific). J. adhaerens colonizes the rocky intertidal area and penetrates into deeper areas only when it lives in association with H. caerulea. The aposymbiotic form of the sponge has not been reported in the bay. To understand the ecological success of this association, we examined the capacity of J. adhaerens to acclimate in Mazatlán Bay using transplant experiments. The transplanted aposymbiotic J. adhaerens did not survive the first 2 weeks; however, J. adhaerens when living in association with H. caerulea, acclimated easily to depth, showing no sign of mortality during the 103 d of the experiment. We conclude that the ability of J. adhaerens to colonize in deeper areas in this hydrodynamic environment may in part rely on the protection provided by the sponge to the algal canopy. Both species contribute to the shape of the associated form. Nevertheless, the morphological variation in the association appears to be dominated by the variation in J. adhaerens canopy to regulate pigment self‐shading under light‐limited conditions and/or tissue resistance under high hydrodynamics. Consequently, our results are consistent with light as the abiotic controlling factor, which regulates the lower depth distribution of the association in Mazatlán Bay, through limiting the growth rate of J. adhaerens. Hydrodynamics may determine the upper limit of the association by imposing high mass losses.     

Peptide N-alkylamides by solid phase synthesis

Three new resins have been developed that allow for the solid phase synthesis of C-terminal peptide N-alkylamides using Boc amino acids, usual side chain protecting groups and hydrogen fluoride cleavage and deprotection. These resins were prepared by reacting the appropriate alkylamine (NH2CH3, NH2CH2CH3, NH2CH2CF3) to Merrifield's 1% divinylbenzene cross-linked chloromethylated polystyrene resin. The application of these resins to the synthesis of C-terminal GnRH N-alkylamides illustrates the versatility of this approach. GnRH analogs were tested for their ability to release LH from cultured rat anterior pituitary cells. [DGlu6, Pro9-NHCH2CH3]-GnRH was synthesized for the first time using the solid phase approach and found to be three times more potent than [DGlu6]-GnRH. Other analogs including [DTrp6, Pro9-NHCH2CH3]-GnRH, [DAla6, Pro9-NHCH2CF3]-GnRH and related peptides were found to be equipotent and to have the same properties (HPLC retention times, amino acid analysis and specific rotation) as the corresponding peptides synthesized using less amenable strategies; yields were equivalent or better than those reported earlier.     

Characterization of the microtubule movement produced by sea urchin egg kinesin

We have used an in vitro assay to characterize some of the motile properties of sea urchin egg kinesin. Egg kinesin is purified via 5'-adenylyl imidodiphosphate-induced binding to taxol-assembled microtubules, extraction from the microtubules in ATP, and gel filtration chromatography (Scholey, J. M., Porter, M. E., Grissom, P. M., and McIntosh, J. R. (1985) Nature 318, 483-486). This partially purified kinesin is then adsorbed to a glass coverslip, mixed with microtubules and ATP, and viewed by video-enhanced differential interference contrast microscopy. The microtubule translocating activity of the purified egg kinesin is qualitatively similar to the analogous activity observed in crude extracts of sea urchin eggs and resembles the activity of neuronal kinesin with respect to both the maximal rate (greater than 0.5 micron/s) and the direction of movement. Axonemes glide on a kinesin-coated coverslip toward their minus ends, and kinesin-coated beads translocate toward the plus ends of centrosome microtubules. Sea urchin egg kinesin is inhibited by high concentrations of SH reagents ([N-ethylmaleimide] greater than 3-5 mM), vanadate greater than 50 microM, and [nonhydrolyzable nucleotides] greater than or equal to [MgATP]. The nucleotide requirement of sea urchin egg kinesin is fairly broad (ATP greater than GTP greater than ITP), and the rate of microtubule movement increases in a saturable fashion with the [ATP]. We conclude that the motile activity of egg kinesin is indistinguishable from that of neuronal kinesin. We propose that egg kinesin may be associated with microtubule-based motility in vivo.     

Water inputs across a tropical montane landscape in Veracruz,Mexico: synergistic effects of land cover,rain and fog seasonality,and interannual precipitation variability

Land‐cover change can alter the spatiotemporal distribution of water inputs to mountain ecosystems, an important control on land‐surface and land‐atmosphere hydrologic fluxes. In eastern Mexico, we examined the influence of three widespread land‐cover types, montane cloud forest, coffee agroforestry, and cleared areas, on total and net water inputs to soil. Stand structural characteristics, as well as rain, fog, stemflow, and throughfall (water that falls through the canopy) water fluxes were measured across 11 sites during wet and dry seasons from 2005 to 2008. Land‐cover type had a significant effect on annual and seasonal net throughfall (NTF <0=canopy water retention plus canopy evaporation; NTF >0=fog water deposition). Forest canopies retained and/or lost to evaporation (i.e. NTF<0) five‐ to 11‐fold more water than coffee agroforests. Moreover, stemflow was fourfold higher under coffee shade than forest trees. Precipitation seasonality and phenological patterns determined the magnitude of these land‐cover differences, as well as their implications for the hydrologic cycle. Significant negative relationships were found between NTF and tree leaf area index (R²=0.38, P<0.002), NTF and stand basal area (R²=0.664, P<0.002), and stemflow and epiphyte loading (R²=0.414, P<0.001). These findings indicate that leaf and epiphyte surface area reductions associated with forest conversion decrease canopy water retention/evaporation, thereby increasing throughfall and stemflow inputs to soil. Interannual precipitation variability also altered patterns of water redistribution across this landscape. Storms and hurricanes resulted in little difference in forest‐coffee wet season NTF, while El Niño Southern Oscillation was associated with a twofold increase in dry season rain and fog throughfall water deposition. In montane headwater regions, changes in water delivery to canopies and soils may affect infiltration, runoff, and evapotranspiration, with implications for provisioning (e.g. water supply) and regulating (e.g. flood mitigation) ecosystem services.     

Genetic differentiation of Elysia timida (Risso, 1818) populations in the Southwest Mediterranean and Mar Menor coastal lagoon

Genetic variation at 10 enzyme loci was analysed in Elysia timida sacoglossan mollusc samples, originating from both coastal lagoon and marine sites. The observed heterozygosity ranged from 0.390 (Los Urrutias) to 0.277 (Tabarca). Marine and coastal lagoon populations were characterised by exclusive alleles.     

Renal cortical intermediary metabolism in the recovery phase of postischemic acute renal failure in the dog.

Renal metabolism has been studied in eight dogs before and 48 hr after a 60-min period of renal ischemia induced by clamping the left renal artery with the simultaneous removal of the right kidney, and in 12 sham-operated animals. The study involved the measurement of renal uptake and production of lactate, glutamine, glutamate, alanine, ammonium, and oxygen, and the measurement of the tissue concentrations of ATP, glutamine, lactate, alpha-ketoglutarate, aspartate, and alanine in the renal cortex. Two days after a temporary renal ischemia, the remaining kidney showed a 22% decrease in glomerular filtration rate (GFR) and a 25% decrease in renal plasma flow. Fractional sodium and potassium excretions were similar to those of control dogs. Renal production or extraction of glutamine, glutamate, alanine, ammonium, and oxygen (all expressed by 100 ml of GFR) was not significantly different in basal conditions or 2 days after ischemia, but lactate extraction was reduced in postischemic kidneys (-101 +/- 29 vs -204 +/- 38 mumol/100 ml GFR in control dogs). The cortical concentrations of glutamine and glutamate were lower in postischemic than in control kidneys. No differences were found in cortical concentration of alpha-ketoglutarate, aspartate, lactate, pyruvate, or ATP, but total nucleotides and inorganic phosphate were decreased in postischemic kidneys. It is concluded that in the recovery phase of the ischemia, a decreased lactate uptake is the main metabolic change, and total ATP production is adapted to the decrease of GFR and sodium reabsorption.     

Ichtyotoxic activity of extracts from Mexican marine macroalgae

Seventy-three species of macroalgae from the Mexican Pacific, Atlantic and Caribbean coast were screened for ichtyotoxic activity. Ethanolic, acetonic and aqueous extracts were prepared and tested against the fish Carassius auratus. The extracts were classified on the basis of their effects as: toxic if the fish died in two hours or less; moderately toxic, if the organism behaved abnormally but death did notoccur, and non-toxic if the fish did not display any change. 79% species were ichtyotoxic to some degree. Extracts of 39 species were toxic, with at least one extract with lethal effects, 19 were moderately toxic and 15 species were non-toxic. Only the extracts ofDictyota bartayresiana, Dictyota cervicornis,Lobophora variegata, Bryothamnion triquetrum and Laurencia obtusa were toxic in all three solvents. The acetone and ethanol extracts were more active, and therefore are more suitable for extraction of toxic substances. This revised version was published online in August 2006 with corrections to the Cover Date.