In vitro studies indicate a quinone is involved in bacterial Mn(II) oxidation
- PDF / 432,279 Bytes
- 11 Pages / 595 x 791 pts Page_size
- 75 Downloads / 140 Views
ORIGINAL PAPER
In vitro studies indicate a quinone is involved in bacterial Mn(II) oxidation Hope A. Johnson · Bradley M. Tebo
Received: 22 January 2007 / Revised: 25 June 2007 / Accepted: 11 July 2007 / Published online: 3 August 2007 © Springer-Verlag 2007
Abstract Manganese(II)-oxidizing bacteria play an integral role in the cycling of Mn as well as other metals and organics. Prior work with Mn(II)-oxidizing bacteria suggested that Mn(II) oxidation involves a multicopper oxidase, but whether this enzyme directly catalyzes Mn(II) oxidation is unknown. For a clearer understanding of Mn(II) oxidation, we have undertaken biochemical studies in the model marine -proteobacterium, Erythrobacter sp. strain SD21. The optimum pH for Mn(II)-oxidizing activity was 8.0 with a speciWc activity of 2.5 nmol £ min¡1 £ mg¡1 and a Km = 204 M. The activity was soluble suggesting a cytoplasmic or periplasmic protein. Mn(III) was an intermediate in the oxidation of Mn(II) and likely the primary product of enzymatic oxidation. The activity was stimulated by pyrroloquinoline quinone (PQQ), NAD+, and calcium but not by copper. In addition, PQQ rescued Pseudomonas putida
Communicated by Friedrich Widdel. H. A. Johnson · B. M. Tebo Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0202, USA H. A. Johnson (&) Joint Center for Structural Genomics, The Scripps Research Institute, 10550 North Torrey Pines Road, sp30-101, La Jolla, CA 92037, USA e-mail: [email protected] Present Address: B. M. Tebo Department of Environmental and Biomolecular Systems, OGI School of Science & Engineering, Oregon Health & Science University, 20000 NW Walker Rd, Beaverton, OR 97006, USA e-mail: [email protected]
MnB1 non Mn(II)-oxidizing mutants with insertions in the anthranilate synthase gene. The substrate and product of anthranilate synthase are intermediates in various quinone biosyntheses. Partially puriWed Mn(II) oxidase was enriched in quinones and had a UV/VIS absorption spectrum similar to a known quinone requiring enzyme but not to multicopper oxidases. These studies suggest that quinones may play an integral role in bacterial Mn(II) oxidation. Keywords Manganese oxidation · PQQ · Erythrobacter · Multicopper oxidase
Introduction It is important to understand the fundamental mechanism of bacterial manganese(II) oxidation because it plays a role in many biogeochemical cycles (Tebo et al. 2004). The amorphous biogenic Mn(IV) oxides produced by Mn(II)-oxidizing bacteria are characterized by their strong reactivity, oxidizing metals and organic molecules such as chromium(III) (Murray and Tebo 2007) and phenolic compounds. In addition to the strong oxidative nature of Mn(IV) oxides, the structure of the oxides leads to the adsorption and sequestration of heavy metals (e.g., Cu, Co, Cd, Zn, Ni, and Pb) resulting in potential applications of Mn(IV) oxides in bioremediation (Tebo et al. 2004). The physiological basis of microbial Mn(II) oxidation remains enigmatic. Many hypothes
Data Loading...
