An Organic Spin Crossover Material in Water from a Covalently Linked Radical Dyad

A covalently linked viologen radical cation dyad acts as a reversible thermomagnetic switch in water. Cycling between diamagnetic and paramagnetic forms by heating and cooling is accompanied by changes in optical and magnetic properties with high radical fidelity. Thermomagnetic switches in water may eventually find use as novel biological thermometers and in temperature-responsive organic materials where the changes in properties originate from a change in electronic spin configuration rather than a change in structure

Highly Divergent Mitochondrial ATP Synthase Complexes in Tetrahymena thermophila

Tetrahymena ATP synthase, an evolutionarily divergent protein complex, has a very unusual structure and protein composition including a unique Fo subunit a and at least 13 proteins with no orthologs outside of the ciliate lineage

A Na+ A1AO ATP synthase with a V-type c subunit in a mesophilic bacterium

A1AO ATP synthases with a V-type c subunit have only been found in hyperthermophilic archaea which makes bioenergetic analyses impossible due to the instability of liposomes at high temperatures. A search for a potential archaeal A1AO ATP synthase with a V-type c subunit in a mesophilic organism revealed an A1AO ATP synthase cluster in the anaerobic, acetogenic bacterium Eubacterium limosum KIST612. The enzyme was purified to apparent homogeneity from cells grown on methanol to a specific activity of 1.2 U·mg−1 with a yield of 12%. The enzyme contained subunits A, B, C, D, E, F, H, a, and c. Subunit c is predicted to be a typical V-type c subunit with only one ion (Na+)-binding site. Indeed, ATP hydrolysis was strictly Na+-dependent. N,N′-dicyclohexylcarbodiimide (DCCD) inhibited ATP hydrolysis, but inhibition was relieved by addition of Na+. Na+ was shown directly to abolish binding of the fluorescence DCCD derivative, NCD-4, to subunit c, demonstrating a competition of Na+ and DCCD/NCD-4 for a common binding site. After incorporation of the A1AO ATP synthase into liposomes, ATP-dependent primary transport of 22Na+ as well as ΔµNa+-driven ATP synthesis could be demonstrated. The Na+ A1AO ATP synthase from E. limosum is the first ATP synthase with a V-type c subunit from a mesophilic organism. This will enable future bioenergetic analysis of these unique ATP synthases