RESUMO
The effect of hydrogen on the rate of phototrophic Fe(II) oxidation by two species of purple bacteria was measured at two different bicarbonate concentrations. Hydrogen slowed Fe(II) oxidation to varying degrees depending on the bicarbonate concentration, but even the slowest rate of Fe(II) oxidation remained on the same order of magnitude as that estimated to have been necessary to deposit the Hamersley banded iron formations. Given the hydrogen and bicarbonate concentrations inferred for the Archean, our data suggest that Fe(II) phototrophy could have been a viable process at this time.
Assuntos
Archaea/metabolismo , Compostos Ferrosos/metabolismo , Hidrogênio/metabolismo , Proteobactérias/metabolismo , Atmosfera , Oxirredução , FotossínteseRESUMO
To probe the structural basis for protein histidine kinase (PHK) catalytic activity and the prospects for PHK-specific inhibitor design, we report the crystal structures for the nucleotide binding domain of Thermotoga maritima CheA with ADP and three ATP analogs (ADPNP, ADPCP and TNP-ATP) bound with either Mg(2+) or Mn(2+). The conformation of ADPNP bound to CheA and related ATPases differs from that reported in the ADPNP complex of PHK EnvZ. Interactions of the active site with the nucleotide gamma-phosphate and its associated Mg(2+) ion are linked to conformational changes in an ATP-lid that could mediate recognition of the substrate domain. The inhibitor TNP-ATP binds CheA with its phosphates in a nonproductive conformation and its adenine and trinitrophenyl groups in two adjacent binding pockets. The trinitrophenyl interaction may be exploited for designing CheA-targeted drugs that would not interfere with host ATPases.
Assuntos
Difosfato de Adenosina/metabolismo , Trifosfato de Adenosina/metabolismo , Proteínas de Bactérias , Proteínas de Membrana/química , Proteínas de Membrana/metabolismo , Proteínas Quinases/química , Proteínas Quinases/metabolismo , Thermotoga maritima/enzimologia , Adenosina Trifosfatases/antagonistas & inibidores , Adenosina Trifosfatases/química , Adenosina Trifosfatases/metabolismo , Trifosfato de Adenosina/análogos & derivados , Sítios de Ligação , Cátions Bivalentes/metabolismo , Cromatografia em Gel , Cristalografia por Raios X , Histidina Quinase , Ligação de Hidrogênio , Magnésio/metabolismo , Proteínas de Membrana/antagonistas & inibidores , Proteínas Quimiotáticas Aceptoras de Metil , Modelos Moleculares , Fosforilação , Inibidores de Proteínas Quinases , Estrutura Terciária de Proteína , SolventesRESUMO
Bacimethrin is an analog of the 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) moiety of thiamine and inhibits the growth of Salmonella enterica serovar Typhimurium on a defined medium. Two classes of mutants that had increased bacimethrin resistance were isolated and characterized. Results showed that overexpression of the thi operon or specific lesions in thiD resulted in a bacimethrin-resistant phenotype. Phenotypic analyses of the thiD mutants suggested that they had a specific defect in one of the two kinase activities associated with this gene product and, further, that ThiD and not PdxK was primarily responsible for salvage of HMP from the medium.
