Identification of two intestinal vitamin D-dependent calcium-binding proteins in the X-linked hypophosphataemic mouse

Two vitamin D-dependent calcium binding proteins (CaBP) of molecular weight approximately 10,000 and 30,000 daltons have been identified in the intestinal mucosal cell cytosol of genetically hypophosphataemic (Hyp) male mice and their normal littermates. Similar amounts of vitamin D-dependent CaBP were found in the two groups of animals. The possible significance of this observation is discussed.     

A new florally dimorphic hexaploid, Echinocereus yavapaiensis sp. nov. (section Triglochidiatus, Cactaceae) from central Arizona

A florally dimorphic hexaploid (n=33), Echinocereus yavapaiensis M. A. Baker, is newly described and possesses the highest number of chromosomes known within the genus. Populations of E. yavapaiensis occur in central Arizona between 1025 and 1860 m elevation and are associated with volcanic bedrock. Fifty three percent of the individuals studied produce only pollen-sterile flowers, which fail to undergo meiosis within the microspore mother cells, while 47% develop only pollen-fertile flowers. Chromosome determinations are presented for 41 populations of Echinocereus, including E. arizonicus (n=11), E. canyonensis (n=22), E. coccineus (n=22), E. matudae (n=11), E. pacificus (n=22), E. mombergerianus (n=22), E. santaritensis (n=22), and E. yavapaiensis. A phenetic analysis compares morphological variability among populations of E. yavapaiensis to those of its closest allies.     

Mutations in Escherichia coli ExbB Transmembrane Domains Identify Scaffolding and Signal Transduction Functions and Exclude Participation in a Proton Pathway

The TonB system couples cytoplasmic membrane proton motive force (pmf) to active transport of diverse nutrients across the outer membrane. Current data suggest that cytoplasmic membrane proteins ExbB and ExbD harness pmf energy. Transmembrane domain (TMD) interactions between TonB and ExbD allow the ExbD C terminus to modulate conformational rearrangements of the periplasmic TonB C terminus in vivo. These conformational changes somehow allow energization of high-affinity TonB-gated transporters by direct interaction with TonB. While ExbB is essential for energy transduction, its role is not well understood. ExbB has N-terminus-out, C-terminus-in topology with three TMDs. TMDs 1 and 2 are punctuated by a cytoplasmic loop, with the C-terminal tail also occupying the cytoplasm. We tested the hypothesis that ExbB TMD residues play roles in proton translocation. Reassessment of TMD boundaries based on hydrophobic character and residue conservation among distantly related ExbB proteins brought earlier widely divergent predictions into congruence. All TMD residues with potentially function-specific side chains (Lys, Cys, Ser, Thr, Tyr, Glu, and Asn) and residues with probable structure-specific side chains (Trp, Gly, and Pro) were substituted with Ala and evaluated in multiple assays. While all three TMDs were essential, they had different roles: TMD1 was a region through which ExbB interacted with the TonB TMD. TMD2 and TMD3, the most conserved among the ExbB/TolQ/MotA/PomA family, played roles in signal transduction between cytoplasm and periplasm and the transition from ExbB homodimers to homotetramers. Consideration of combined data excludes ExbB TMD residues from direct participation in a proton pathway.     

Analysis and purification of acyl coenzyme A thioesters by reversed-phase ion-pair liquid chromatography.

A rapid method is described for the analysis of mixtures of short-chain acyl coenzyme A thioesters by reversed-phase ion-pair chromatography on LiChrosorb RP-8 and μBondapak C₁₈ columns. The technique is applicable to separation of CoASH, acetyl-CoA propionyl-CoA, and 3-hydroxy-3-methylglutaryl-CoA, as well as dicarboxylic acids and several nucleotides commonly used as cofactors for biosynthetic reactions. The method was utilized on a preparative scale for purification of 3-hydroxy-3-ethylglutaryl-CoA from CoASH and 3-hydroxy-3-ethylglutaric acid. The counterion employed was tetrabutylammonium (phosphate), pH 5.5, in various methanol:water mixtures. Elution profiles and retention values of compounds were influenced by the concentration of counterion and mass of injected sample. Tetrabutylammonium ions could be removed from effluent by ionexchange chromatography on Amberlite IR-120 resin.     

Tourism’s nitrogen footprint on a Mesoamerican coral reef

Globally, the eutrophication of coastal marine environments is a worsening problem that is accelerating the loss of biodiversity and ecosystem services. Coral reefs are among the most sensitive to this change, as chronic inputs of agricultural and wastewater effluents and atmospheric deposition disrupt their naturally oligotrophic state. Often, anthropogenic alteration of the coastal nitrogen pool can proceed undetected as rapid mixing with ocean waters can mask chronic and ephemeral nitrogen inputs. Monitoring nitrogen stable isotope values (δ ¹⁵N) of benthic organisms provides a useful solution to this problem. Through a 7-yr monitoring effort in Quintana Roo, Mexico, we show that δ ¹⁵N values of the common sea fan Gorgonia ventalina were more variable near a developed (Akumal) site than at an undeveloped (Mahahual) site. Beginning in 2007, the global recession decreased tourist visitations to Akumal, which corresponded with a pronounced 1.6 ‰ decline in sea fan δ ¹⁵N through 2009, at which time δ ¹⁵N values were similar to those from Mahahual. With the recovery of tourism, δ ¹⁵N values increased to previous levels. Overall, 84 % of the observed variation in δ ¹⁵N was explained by tourist visitations in the preceding year alone, indicating that variable nitrogen source contributions are correlated with sea fan δ ¹⁵N values. We also found that annual precipitation accounted for some variation in δ ¹⁵N, likely due to its role in groundwater flushing into the sea. Together, these factors accounted for 96 % of the variation in δ ¹⁵N. Using a mixing model, we estimate that sewage can account for up to 42 % of nitrogen in sea fan biomass. These findings illustrate the high connectivity between land-based activities and coral reef productivity and the measurable impact of the tourism industry on the ecosystem it relies on.