, 2003), this value is, however, likely to be an underestimate. It is interesting to compare the kinetic behavior with that observed for the related DMS dehydrogenase of R. sulfidophilum. In this case, Creevey et al. (2008) investigated the interaction
between cytochrome c2 and DMS reductase and found a KM value of 21 μM (Creevey et al., 2008). The present observations with chlorate reductase are consistent with a KM value in this range. Moreover, Chang et al. (2010) investigated the electron transfer between the cbb3-type oxygen reductase and the soluble diheme cytochrome c4 in Vibrio cholerae. They conclude that a concentration of cytochrome c4 as high as 100 μM does not saturate the oxidase activity. In this case, it is suggested that
the activity is competitively inhibited by the oxidized product due to its similar affinity PI3K inhibitor to the redox partner (Chang et al., 2010). A high KM value can be the result of a fast off-rate for the substrate and thus a relatively low affinity, or of the reaction step subsequent to substrate binding being fast. Because this step would be an electron transfer from the reduced substrate to one of the redox centers in chlorate reductase, the latter alternative is a possible explanation. However, a more detailed Selleck PI3K Inhibitor Library kinetic characterization is required to understand the interaction between the enzyme and its electron donor substrate. In conclusion we have, using the purified reactants, demonstrated that the soluble 9-kDa cytochrome c-Id1 of I. dechloratans serves as an electron donor for its soluble periplasmic chlorate reductase. The route for electron transport in this case is thus more
similar to that observed with DMS dehydrogenase and selenate reductase than with electron transfer to (per)chlorate reductases in Dechloromonas species (Bender et al., 2005). This is consistent with the notion of I. dechloratans reductase being more closely related to DMS dehydrogenase and selenate reductase than to (per)chlorate reductase of Dechloromonas Flucloronide species. We thank Proteomics Core Facility at University of Gothenburg, especially Carina Sihlbom, for running the MS analysis. We also thank Dr Maria Rova for helpful comments and suggestions regarding the manuscript. “
“Vibrio cholerae, the causative agent of cholera and a natural inhabitant of aquatic environments, regulates numerous behaviors using a quorum-sensing (QS) system conserved among many members of the marine genus Vibrio. The Vibrio QS response is mediated by two extracellular autoinducer (AI) molecules: CAI-I, which is produced only by Vibrios, and AI-2, which is produced by many bacteria. In marine biofilms on chitinous surfaces, QS-proficient V. cholerae become naturally competent to take up extracellular DNA. Because the direct role of AIs in this environmental behavior had not been determined, we sought to define the contribution of CAI-1 and AI-2 in controlling transcription of the competence gene, comEA, and in DNA uptake.