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Bradley, JM, Svistunenko DA, Pullin J, Hill N, Stuart RK, Palenik B, Wilson MT, Hemmings AM, Moore GR, Le Brun NE.  2019.  Reaction of O-2 with a diiron protein generates a mixed-valent Fe2+/Fe3+ center and peroxide. Proceedings of the National Academy of Sciences of the United States of America. 116:2058-2067.   10.1073/pnas.1809913116   AbstractWebsite

The gene encoding the cyanobacterial ferritin SynFtn is up-regulated in response to copper stress. Here, we show that, while SynFtn does not interact directly with copper, it is highly unusual in several ways. First, its catalytic diiron ferroxidase center is unlike those of all other characterized prokaryotic ferritins and instead resembles an animal H-chain ferritin center. Second, as demonstrated by kinetic, spectro-scopic, and high-resolution X-ray crystallographic data, reaction of O-2 with the di-Fe2+ center results in a direct, one-electron oxidation to a mixed-valent Fe2+/Fe3+ form. Iron-O-2 chemistry of this type is currently unknown among the growing family of proteins that bind a diiron site within a four alpha-helical bundle in general and ferritins in particular. The mixed-valent form, which slowly oxidized to the more usual di-Fe3+ form, is an intermediate that is continually generated during mineralization. Peroxide, rather than superoxide, is shown to be the product of O-2 reduction, implying that ferroxidase centers function in pairs via long-range electron transfer through the protein resulting in reduction of O-2 bound at only one of the centers. We show that electron transfer is mediated by the transient formation of a radical on Tyr40, which lies similar to 4 angstrom from the diiron center. As well as demonstrating an expansion of the iron-O-2 chemistry known to occur in nature, these data are also highly relevant to the question of whether all ferritins mineralize iron via a common mechanism, providing unequivocal proof that they do not.

Bradley, JM, Hill N, Le Brun NE, Stuart RK, Palenik B.  2014.  Spectroscopic investigation of iron mineralisation by a cyanobacterial ferritin. Journal of Biological Inorganic Chemistry. 19:S291-S291. AbstractWebsite
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de la Broise, D, Palenik B.  2007.  Immersed in situ microcosms: A tool for the assessment of pollution impact on phytoplankton. Journal of Experimental Marine Biology and Ecology. 341:274-281.   10.1016/j.jembe.2006.10.045   AbstractWebsite

In situ phytoplankton microcosms were developed and characterized for use in toxicity testing. The microcosms contained 225 mu m filtered seawater maintained in 1 liter glass bottles attached to a plastic frame and immersed at 3 in under the sea surface. Synechococcus and picoeukaryote population dynamics in microcosms and the surrounding water were compared. A bloom-like behaviour observed for Synechococcus in these phytoplankton microcosms was avoided when 10% of the culture volume was replaced, every two days, by filtered seawater. After 2 weeks, no significant difference in Synechococcus and picoeukaryotes cell counts was observed in microcosms compared to the surrounding free seawater. Synechococcus fluorescence at 545 nm (phycoerythrobilin) fluctuated with a similar pattern in such microcosms and in free seawater and were shown to be correlated to light intensity fluctuations over a two week experiment. The in situ microcosms were used to study the impact of low copper additions. Synechococcus populations were dramatically decreased by copper addition, while picoeukaryote populations were increased simultaneously. Our data show that drastic changes in species composition can occur at copper concentrations encountered in polluted coastal areas. (c) 2006 Elsevier B.V. All rights reserved.