Kinetics of reduction of Fe(III) complexes by outer membrane cytochromes MtrC and OmcA of Shewanella oneidensis MR-1.
Because of their cell surface locations, the outer membrane c-type cytochromes MtrC and OmcA of Shewanella oneidensis MR-1 have been suggested to be the terminal reductases for a range of redox-reactive metals that form poorly soluble solids or that do not readily cross the outer membrane. In this work, we determined the kinetics of reduction of a series of Fe(III) complexes with citrate, nitrilotriacetic acid (NTA), and EDTA by MtrC and OmcA using a stopped-flow technique in combination with theoretical computation methods. Stopped-flow kinetic data showed that the reaction proceeded in two stages, a fast stage that was completed in less than 1 s, followed by a second, relatively slower stage. For a given complex, electron transfer by MtrC was faster than that by OmcA. For a given cytochrome, the reaction was completed in the order Fe-EDTA > Fe-NTA > Fe-citrate. The kinetic data could be modeled by two parallel second-order bimolecular redox reactions with second-order rate constants ranging from 0.872 microM(-1) s(-1) for the reaction between MtrC and the Fe-EDTA complex to 0.012 microM(-1) s(-1) for the reaction between OmcA and Fe-citrate. The biphasic reaction kinetics was attributed to redox potential differences among the heme groups or redox site heterogeneity within the cytochromes. The results of redox potential and reorganization energy calculations showed that the reaction rate was influenced mostly by the relatively large reorganization energy. The results demonstrate that ligand complexation plays an important role in microbial dissimilatory reduction and mineral transformation of iron, as well as other redox-sensitive metal species in nature.
Wang
Zheming
Z
Pacific Northwest National Laboratory, Richland, WA 99352, USA. Zheming.wang@pnl.gov
Liu
Chongxuan
C
Wang
Xuelin
X
Marshall
Matthew J
MJ
Zachara
John M
JM
Rosso
Kevin M
KM
Dupuis
Michel
M
Fredrickson
James K
JK
Heald
Steve
S
Shi
Liang
L
D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism; D004492:Edetic Acid / Q000378:metabolism; D005290:Ferric Compounds / Q000378:metabolism*; D007700:Kinetics; D009571:Nitrilotriacetic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D020592:Shewanella / Q000378:metabolism*
D001425:Bacterial Outer Membrane Proteins; D003574:Cytochrome c Group; D003580:Cytochromes; D005290:Ferric Compounds; C025314:ferric citrate; D004492:Edetic Acid; C433527:MtrC protein, Shewanella; D009571:Nitrilotriacetic Acid; C019179:Fe(III)-EDTA; C020326:ferric nitrilotriacetate
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