Plastocyanin Binding to Photosystem I as a Function of the Charge State of the Metal Ion: Effect of Metal Site Conformation
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- 作者：Eva Danielsen ; Henrik Vibe Scheller ; Rogert Bauer ; Lars Hemmingsen ; Morten Jannik Bjerrum ; and Ö ; rjan Hansson
- 刊名：Biochemistry
- 出版年：1999
- 出版时间：August 31, 1999
- 年：1999
- 卷：38
- 期：35
- 页码：11531 - 11540
- 全文大小：116K
- 年卷期：v.38,no.35(August 31, 1999)
- ISSN：1520-4995
文摘
The binding of Ag- and Cd-substituted plastocyanin to reduced photosystem 1 of spinach hasbeen studied through the rotational correlation time of plastocyanin measured by the technique of perturbedangular correlation of 
-rays (PAC). Ag and Cd are used as models for native Cu(I) and Cu(II), respectively.A dissociation constant of 5 
M was found for Ag-plastocyanin, whereas the dissociation constant wasat least 24 times higher for Cd-plastocyanin. PAC was further used to characterize the structure of themetal site of Cd- and Ag-plastocyanin. The Cd spectra are characteristic of a planar configuration of onecysteine and two histidines. However, the spectra show an unusual peak broadening and a high degree ofinternal motion, interpreted as motion of one of the histidines within the plane. 111Ag decays to 111Cd,followed by the emission of two -rays used for the PAC experiment. The 111Ag PAC spectra indicatethat one of the coordinating histidines has a different position in the Ag protein than in the Cd protein butthat the decay of Ag to Cd causes a relaxation of the position of this histidine to the position in the Cdprotein within 20 ns. Binding of Ag-plastocyanin to photosystem I stabilized the Ag metal site structureso that no relaxation was observed on a time scale of 100 ns. This stabilization of the Ag structure uponbinding indicates that the metal site structure is involved in regulating how the dissociation constant forplastocyanin depends on the charge of the metal ion.
-rays (PAC). Ag and Cd are used as models for native Cu(I) and Cu(II), respectively.A dissociation constant of 5 M was found for Ag-plastocyanin, whereas the dissociation constant wasat least 24 times higher for Cd-plastocyanin. PAC was further used to characterize the structure of themetal site of Cd- and Ag-plastocyanin. The Cd spectra are characteristic of a planar configuration of onecysteine and two histidines. However, the spectra show an unusual peak broadening and a high degree ofinternal motion, interpreted as motion of one of the histidines within the plane. 111Ag decays to 111Cd,followed by the emission of two -rays used for the PAC experiment. The 111Ag PAC spectra indicatethat one of the coordinating histidines has a different position in the Ag protein than in the Cd protein butthat the decay of Ag to Cd causes a relaxation of the position of this histidine to the position in the Cdprotein within 20 ns. Binding of Ag-plastocyanin to photosystem I stabilized the Ag metal site structureso that no relaxation was observed on a time scale of 100 ns. This stabilization of the Ag structure uponbinding indicates that the metal site structure is involved in regulating how the dissociation constant forplastocyanin depends on the charge of the metal ion.