Impact of Mutations within the Putative Ca2+-Binding Lumenal Interhelical a-b Loop of the Photosystem II D1 Protein on the Kinetics of Photoactivation and H2O-Oxidation in Syn
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- 作者：Ming Qian ; Luan Dao ; Richard J. Debus ; and Robert L. Burnap
- 刊名：Biochemistry
- 出版年：1999
- 出版时间：May 11, 1999
- 年：1999
- 卷：38
- 期：19
- 页码：6070 - 6081
- 全文大小：158K
- 年卷期：v.38,no.19(May 11, 1999)
- ISSN：1520-4995
文摘
Mutations D1-D59N and D1-D61E in the putative Ca2+-binding lumenal interhelical a-bloop of the photosystem II (PSII) D1 protein [Chu, H. A., Nguyen, A. P., and Debus (1995), Biochemistry34, 5839-5858] were further characterized in terms of S-state cycling and photoactivation. Bare platinumelectrode measurements of centrifugally deposited O2-evolving membranes isolated from the a-b loopmutants demonstrated a retarded appearance of O2 following single turnover flashes, although not to theextent of retardation seen in the 
psb0 mutant, which lacks the extrinsic manganese-stabilizing protein(MSP). Double flash measurements indicate that retarded O2 release in mutants coincides with a decreasein overall PSII turnover during the S3-[S4]-S0 transition. S2 and S3 decay measurements in the isolatedmembranes indicate that D1-D59N and D1-D61E have faster decays of these higher S-states in contrastto slowed decays in the psb0 mutant. Measurements of the flash interval dependence of photoactivationindicate that intermediates of photoactivation [light-dependent assembly of the (Mn)4 complex] are highlydestabilized in the a-b loop mutants compared to both psbO and the wild-type: flash intervals of greaterthan 2 s result in the nearly complete decay of unstable photointermediate(s) in the D1-D59N and D1-D61E samples, whereas a similar loss does not occur until intervals even greater than 10 s in the psbOand wild-type samples. These results are consistent with a role for the residues D1-D59 and D1-D61in modulating the redox properties of the higher S-states and, also, possibly in the binding the calciumion involved in photoactivation.
psb0 mutant, which lacks the extrinsic manganese-stabilizing protein(MSP). Double flash measurements indicate that retarded O2 release in mutants coincides with a decreasein overall PSII turnover during the S3-[S4]-S0 transition. S2 and S3 decay measurements in the isolatedmembranes indicate that D1-D59N and D1-D61E have faster decays of these higher S-states in contrastto slowed decays in the psb0 mutant. Measurements of the flash interval dependence of photoactivationindicate that intermediates of photoactivation [light-dependent assembly of the (Mn)4 complex] are highlydestabilized in the a-b loop mutants compared to both psbO and the wild-type: flash intervals of greaterthan 2 s result in the nearly complete decay of unstable photointermediate(s) in the D1-D59N and D1-D61E samples, whereas a similar loss does not occur until intervals even greater than 10 s in the psbOand wild-type samples. These results are consistent with a role for the residues D1-D59 and D1-D61in modulating the redox properties of the higher S-states and, also, possibly in the binding the calciumion involved in photoactivation.