The Single Superoxide Dismutase of Rhodobacter capsulatus Is a Cambialistic, Manganese-Containing Enzyme

Abstract

The phototrophic bacterium Rhodobacter capsulatus contains a single, oxygen-responsive superoxide dismutase (SOD Rc ) homologous to iron-containing superoxide dismutase enzymes. Recombinant SOD Rc , however, displayed higher activity after refolding with Mn 2؉ , especially when the pH of the assay mixture was raised. SOD Rc isolated from Rhodobacter cells also preferentially contains manganese, but metal discrimination depends on the culture conditions, with iron fractions increasing from 7% in aerobic cultures up to 40% in photosynthetic cultures. Therefore, SOD Rc behaves as a Mn-containing dismutase with cambialistic properties.

Some thoughts on the concept of colimitation: Three definitions and the importance of bioavailability

“…Two of the best studied examples of this type of system in phytoplankton are (1) the carbonic anhydrases in the marine diatoms that can utilize zinc, cobalt, or cadmium (e.g., Morel et al 1994;Sunda and Huntsman 1995a;Lane et al 2005), and (2) a variety of superoxide dismutases (SODs) that contain Ni, Mn, Fe, or both Cu and Zn in their active sites (see Wolfe-Simon et al 2005 and references therein). Biochemical (cambialistic) substitution has also been observed for Mn and Fe within a single SOD enzyme (Sugio et al 2000;Tabares et al 2003;WolfeSimon et al 2005), although this substitution does not appear to be present in marine phytoplankton: the diatoms and cyanobacteria examined appear to rely on MnSOD or NiSOD, respectively (Peers and Price 2004;Wolfe-Simon et al 2005;Dupont et al 2006). We have previously used three-dimensional (3D) representations of growth-rate data for cobalt and zinc culture experiments as a means to intuitively display this type II biochemical substitution effect (Saito 2001;Saito et al 2002Saito et al , 2003.…”

“…Enzymes with this characteristic are termed cambialistic (Sugio et al 2000;Tabares et al 2003;Wolfe-Simon et al 2005). In addition, multiple forms of enzymes with equivalent functionalities but with different metals in the active site can co-occur within an organism.…”

Superoxide Generation by Chlorophyllide a Reductase of Rhodobacter sphaeroides

“…Consistently, no COR activity was found under the gas phase of O 2 higher than 5% (DO higher than 65 Ϯ 6 M). However, ϳ33% enzyme activity (15.9 Ϯ 2.6 nmol/min/mg protein) was reproducibly observed under the gas phase of 2% O 2 at low O 2 . Indeed, the half-life of BchXYZ complex, which had been sparged with 2% O 2 (DO, 42 Ϯ 6 M), was ϳ210 min (Fig.…”

“…The role of CuZn-SOD in protecting the photoheterotrophic cells from periplasmic superoxide upon exposure to O 2 was proposed (1). A cambialistic SOD using manganese or iron is the only SOD found in Rhodobacter capsulatus and is essential for cell viability (2,3). Oxidative stress defense in R. sphaeroides and R. capsulatus is also mediated by catalases as well as by glutathione-glutaredoxin and thioredoxin systems that act as thiol-disulfide redox buffer to reduce the protein thiols that were oxidized (4,5).…”

Cellular Iron Distribution in Bacillus anthracis

“…Recombinant proteins SodA1 and SodA2 were gifts provided by M. J. Fogg and A. J. Wilkinson, University of York, United Kingdom (9). On receipt, aliquots were diluted to a 1 M final concentration in 2% HNO 3 and analyzed by ICP-MS. Apo, Mn 2ϩ , and Fe 2ϩ forms were prepared using published protocols (37,47). To obtain apoproteins, native enzymes (1.5 ml at 25 M) were denatured in 50 mM Tris (pH 7.8)-8 M urea-10 mM EDTA and then renatured by dialysis twice against 1 liter of 50 mM Tris buffer (pH 7.8)-10 mM EDTA.…”