The Kdp-ATPase of Escherichia coli

The kdpFABC operon of Escherichia coli consists of the four structural genes kdpF, kdpA, kdpB, and kdpC. Expression of the kdpF gene was demonstrated using minicells of E. coli. In addition, it was shown that the KdpF subunit remains associated with the purified complex. Although KdpF is not essential in vivo, the purified complex lacking KdpF exhibits hardly any K+-stimulated ATPase activity. This clearly demonstrates that the KdpF subunit is stabilizing the transport complex. Charge translocation by the purified Kdp-ATPase was measured with the potential-sensitive dye DiSC3(5) using proteoliposomes. Upon addition of ATP a fluorescence quench was observed indicating the buildup of a negative potential inside the proteoliposomes. Using the Kdp-ATPase derived from a mutant strain, in which the Km value for K+ (1,2 mM) was almost identical to that of Rb+ (1.4 mM), the same fluorescence quench was observed when K+ or Rb+ were present in the lumen of the proteoliposomes. These data clearly indicate that the Kdp-ATPase transports K+ in an electrogenic manner. In order to identify the binding site(s) for the inhibitor concanamycin A within the Kdp complex, concanamycin A was synthesized. Using this compound labeling of KdpA and KdpB, but not of KdpC, could be shown with the purified complex. When everted vesicles were used only KdpB could be labeled

Efficient Dehydrogenation of Formic Acid Using an Iron Catalyst

Hydrogen is one of the essential reactants in the chemical industry, though its generation from renewable sources and storage in a safe and reversible manner remain challenging. Formic acid (HCO2H or FA) is a promising source and storage material in this respect. Here, we present a highly active iron catalyst system for the liberation of H2 from FA. Applying 0.005 mole percent of Fe(BF4)2·6H2O and tris[(2-diphenylphosphino)ethyl]phosphine [P(CH2CH2PPh2)3, PP3] to a solution of FA in environmentally benign propylene carbonate, with no further additives or base, affords turnover frequencies up to 9425 per hour and a turnover number of more than 92,000 at 80°C. We used in situ nuclear magnetic resonance spectroscopy, kinetic studies, and density functional theory calculations to explain possible reaction mechanisms