Journal article
Light-driven oxygen production from superoxide by Mn-binding bacterial reaction centers
Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604, USA. JAllen@asu.edu1
One of the outstanding questions concerning the early Earth is how ancient phototrophs made the evolutionary transition from anoxygenic to oxygenic photosynthesis, which resulted in a substantial increase in the amount of oxygen in the atmosphere. We have previously demonstrated that reaction centers from anoxygenic photosynthetic bacteria can be modified to bind a redox-active Mn cofactor, thus gaining a key functional feature of photosystem II, which contains the site for water oxidation in cyanobacteria, algae, and plants [Thielges M, et al. (2005) Biochemistry 44:7389-7394].
In this paper, the Mn-binding reaction centers are shown to have a light-driven enzymatic function; namely, the ability to convert superoxide into molecular oxygen. This activity has a relatively high efficiency with a k(cat) of approximately 1 s(-1) that is significantly larger than typically observed for designed enzymes, and a K(m) of 35-40 μM that is comparable to the value of 50 μM for Mn-superoxide dismutase, which catalyzes a similar reaction.
Unlike wild-type reaction centers, the highly oxidizing reaction centers are not stable in the light unless they have a bound Mn. The stability and enzymatic ability of this type of Mn-binding reaction centers would have provided primitive phototrophs with an environmental advantage before the evolution of organisms with a more complex Mn(4)Ca cluster needed to perform the multielectron reactions required to oxidize water.
Language: | English |
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Publisher: | National Academy of Sciences |
Year: | 2012 |
Pages: | 2314-2318 |
ISSN: | 10916490 and 00278424 |
Types: | Journal article |
DOI: | 10.1073/pnas.1115364109 |