The conformation of apamin

AbstractEnergy minimisation techniques are used as a tool to distinguish between different proposed models for the structure of the bee venom polypeptide apamin. The influence of electrostatic interactions on the resultant energies is noted. The model of Hider and Ragnarsson [(1980) FEBS Lett. 111, 189-193] is found to be of consistently low energy

The iron-binding properties of aminochelin, the mono(catecholamide) siderophore of Azotobacter vinelandii

Azotobacter vinelandii produces siderophores with different metal-binding properties, depending on the concentration of Fe(III) and molybdate in the growth medium. The three protonation constants of the mono(catecholamide) siderophore aminochelin were determined by simultaneous spectrophotometric and potentiometric titrations as log K 1=12.1, log K 2=10.22 and log K 3=7.04. Based on the two catechol protonation constants, log K 1 and log K 3, the overall stability constant of the aminochelin iron 3:1 complex was found to be log ß 3=41.3, resulting in a pFe 3+ value of 17.6 at pH 7.45. In order to further investigate the properties of the siderophore, the solubilization of Fe(III) hydroxide by a 8×10 –4 M solution of aminochelin at pH 7 and 25 °C was followed spectrophotometrically in the absence and in the presence of molybdate. It was observed that the addition of molybdate resulted in a significant delay in the solubilization

Effect of iron chelation on anti-pseudomonal activity of doxycycline

BACKGROUND: Increasing resistance of microorganisms to antimicrobial agents is a growing concern and there is a lack of novel agents. This has stimulated the exploration of novel strategies for treatment of infection. OBJECTIVE: To investigate synergistic interactions between five tetracyclines and tobramycin with an iron chelator (CP762) against two reference strains and nine clinical isolates of Pseudomonas aeruginosa from cystic fibrosis patients. METHOD: Microdilution assays for minimal inhibitory concentration determination and checkerboard assays were used to assess synergy between antibiotics and CP762. Given the iron-binding capacity of tetracyclines, the binding of iron with doxycycline was investigated using Job's plot methodology. Synergy between the iron-bound form of doxycycline and CP762 was compared with that of unbound doxycycline and CP762. Enhancement of doxycycline anti-biofilm activity was also assessed. RESULTS: There was synergy between CP762 and all tetracyclines, except minocycline, against the reference strains but that against clinical isolates was variable. Synergy was not demonstrated for tobramycin against any of the strains tested. This led to the hypothesis that iron chelation preserves the binding of tetracyclines to the bacterial ribosome. Susceptibility to iron-bound doxycycline was decreased by two- to four-fold and synergistic interactions with the iron chelator were consistently more intense with iron-bound doxycycline than with doxycycline alone. The doxycycline–iron chelator combination also significantly reduced cell viability in established biofilms. CONCLUSION: The data in this study provide evidence that iron chelation enhances the anti-pseudomonal activity of tetracyclines, specifically doxycycline