GEOC 76 |
| Sergei V. Baranov1, Alexei M. Tyryshkin1, Jyotishman Dasgupta1, Richard K. Watt1, Yuri N. Kozlov2, A. A. Kazakova2, Vyacheslav V. Klimov2, and Charles Dismukes1. (1) Department of Chemistry, Princeton University, 7 Hoyt Laboratory, Princeton, NJ 08544, (2) Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, 142290, Russia |
| Oxidation of Mn2+ by anoxygenic photosynthetic bacteria assisted by bicarbonate is hypothesized to be the biological innovation that led to the evolution of oxygenic photosynthesis. In vitro electrochemistry and EPR studies on isolated Photosynthetic Reaction Centers (PSII) have been used to examine this complex process. Results show that bicarbonate complexation to Mn2+ greatly favors the oxidation to Mn3+(E0=0.67V & 0.52V for 1:1& 1:2 complex respectively compared to E0=1.2V of aquo-Mn2+). The electron transport rate of Mn2+ to apo-PSII (depleted of Mn4-cluster, Ca2+ and Cl-) is accelerated by bicarbonate. Electron donation requires formation of a ternary complex (apoPSII-Mn2+-HCO3-) that is photooxidized to a Mn3+ ternary complex. EPR of the Mn3+ complex shows that bicarbonate binding causes substantial changes in both the ligand field strength and 55Mn magnetic hyperfine interaction. This work reveals both structural and thermodynamic basis for involvement of bicarbonate in the assembly of the Mn4-cluster in PSII. |
|
Microbially Mediated Manganese and Iron Oxidation in the Biosphere
1:30 PM-5:05 PM, Tuesday, March 30, 2004 Marriott -- Marquis NE, Oral
Division of Geochemistry |