A self-assembling fluorescent dipeptide conjugate for cell labelling

Derivatives of fluorophore FITC (fluorescein isothiocyanate) are widely used in bioassays to label proteins and cells. An N-terminal leucine dipeptide is attached to FITC, and we show that this simple conjugate molecule is cytocompatible and is uptaken by cells (human dermal and corneal fibroblasts) in contrast to FITC itself. Co-localisation shows that FITC-LL segregates in peri-nuclear and intracellular vesicle regions. Above a critical aggregation concentration, the conjugate is shown to self-assemble into beta-sheet nanostructures comprising molecular bilayers

Silicon and zinc biogeochemical cycles coupled through the Southern Ocean

Zinc is vital for the physiology of oceanic phytoplankton. The striking similarity of the depth profiles of zinc to those of silicate suggests that the uptake of both elements into the opaline frustules of diatoms, and their regeneration from these frustules, should be coupled. However, the zinc content of diatom opal is negligible, and zinc is taken up into and regenerated from the organic parts of diatom cells. Thus, since opaline frustules dissolve deep in the water column while organic material is regenerated in the shallow subsurface ocean, there is little reason to expect the observed close similarity between zinc and silicate, and the dissimilarity between zinc and phosphate. Here we combine observations with simulations using a three-dimensional model of ocean circulation and biogeochemistry to show that the coupled distribution of zinc and silicate, as well as the decoupling of zinc and phosphate, can arise in the absence of mechanistic links between the uptake of zinc and silicate, and despite contrasting regeneration length scales. Our simulations indicate that the oceanic zinc distribution is, in fact, a natural result of the interaction between ocean biogeochemistry and the physical circulation through the Southern Ocean hub. Our analysis demonstrates the importance of uptake stoichiometry in controlling ocean biogeochemistry, and the utility of global-scale elemental covariation in the ocean in understanding these controls