Kinetic Performance and Energy Profile in a Roller Coaster Electron Transfer Chain: A Study of Modified Tetraheme-Reaction Center Constructs

详细信息    查看全文

• 作者：Jean Alric ; Jé ; rô ; me Lavergne ; Fabrice Rappaport ; André ; Vermé ; glio ; Katsumi Matsuura ; Keizo Shimada ; and Kenji V. P. Nagashima
• 刊名：Journal of the American Chemical Society
• 出版年：2006
• 出版时间：March 29, 2006
• 年：2006
• 卷：128
• 期：12
• 页码：4136 - 4145
• 全文大小：270K
• 年卷期：v.128,no.12(March 29, 2006)
• ISSN：1520-5126

文摘

In many electron-transfer proteins, the arrangement of cofactors implies a succession of uphilland downhill steps. The kinetic implications of such arrangements are examined in the present work, basedon a study of chimeric photosynthetic reaction centers obtained by expressing the tetraheme subunit fromBlastochloris viridis in another purple bacterium, Rubrivivax gelatinosus. Site-directed mutations of theenvironment of heme c₅₅₉, which is the immediate electron donor to the primary donor P, inducedmodifications of this heme's midpoint potential over a range of 400 mV. This resulted in shifts of the apparentmidpoint potentials of the neighboring carriers, yielding estimates of the interactions between redox centers.At both extremities of the explored range, the energy profile of the electron-transfer chain presented anadditional uphill step, either downstream or upstream from c₅₅₉. These modifications caused conspicuouschanges of the electron-transfer rate across the tetraheme subunit, which became ~100-fold slower in themutants where the midpoint potential of c₅₅₉ was lowest. A theoretical analysis of the kinetics is presented,predicting a displacement of the rate-limiting step when lowering the potential of c₅₅₉. A reasonable agreementwith the data was obtained when combining this treatment with the rates predicted by electron transfertheory for the individual rate constants.