Systematic design of chemical oscillators using complexation and precipitation equilibria

Concentration oscillations are ubiquitous in living systems, where they involve a wide range of chemical species. In contrast, early in vitro chemical oscillators were all derived from two accidentally discovered reactions based on oxyhalogen chemistry. Over the past 25 years, the use of a systematic design algorithm, in which a slow feedback reaction periodically drives a bistable system in a flow reactor between its two steady states, has increased the list of oscillating chemical reactions to dozens of systems. But these oscillating reactions are still confined to a handful of elements that possess multiple stable oxidation states: halogens, sulphur and some transition metals. Here we show that linking a 'core' oscillator to a complexation or precipitation equilibrium can induce concentration oscillations in a species participating in the equilibrium. We use this method to design systems that produce periodic pulses of calcium, aluminium or fluoride ions. The ability to generate oscillations in elements possessing only a single stable oxidation state (for example, Na+, F-, Ca2+) may lead to reactions that are useful for coupling to or probing living systems, or that help us to understand new mechanisms by which periodic behaviour may arise.     

Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation

Giardia intestinalis (syn. lamblia) is one of the most widespread intestinal protozoan pathogens worldwide, causing hundreds of thousands of cases of diarrhoea each year. Giardia is a member of the diplomonads, often described as an ancient protist group whose primitive nature is suggested by the lack of typical eukaryotic organelles (for example, mitochondria, peroxisomes), the presence of a poorly developed endomembrane system and by their early branching in a number of gene phylogenies. The discovery of nuclear genes of putative mitochondrial ancestry in Giardia and the recent identification of mitochondrial remnant organelles in amitochondrial protists such as Entamoeba histolytica and Trachipleistophora hominis suggest that the eukaryotic amitochondrial state is not a primitive condition but is rather the result of reductive evolution. Using an in vitro protein reconstitution assay and specific antibodies against IscS and IscU--two mitochondrial marker proteins involved in iron-sulphur cluster biosynthesis--here we demonstrate that Giardia contains mitochondrial remnant organelles (mitosomes) bounded by double membranes that function in iron-sulphur protein maturation. Our results indicate that Giardia is not primitively amitochondrial and that it has retained a functional organelle derived from the original mitochondrial endosymbiont.