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Recently, construction of strains of Synechocystis sp. PCC6803 having a His6 extension (His-tag) of the carboxyl terminus of the CP47 protein has been reported (T.M. Bricker et al, Biochim. Biophys. Acta 1409 (1998) 50; M.J. Reifler et al., in: Garab, Pusztai (Eds.) Proc. XIth International Congress on Photosynthesis, 1998). While these initial reports suggest a minimal impact of the His-tag upon Photosystem (PS) II function, a more thorough analysis of the kinetic properties of the modified complex is essential. This communication reports on a more detailed kinetic analysis to assess possible perturbations of PS II due to the genetic addition of the His-tag on the CP47 protein. It was found that: (1) Patterns of flash O2 yield exhibited normal period four oscillations and the associated fits of the Kok-Joliot S-state cycling parameters were virtually identical to the wild type; (2) O2 release kinetics during the S3-S0 transition were experimentally indistinguishable from the wild type; (3) S-state decay measurements indicate slightly faster decays of the S2 and S3 states compared to the wild type; (4) fluorescence measurements indicate that the kinetics of the forward reaction of electron transfer from Q(A)/- to Q(B) and back-reactions of Q(A)/- with PS II electron donors are similar in the His-tag and wild-type strains. It is therefore concluded that the addition of the His-tag results in a minimal perturbation of PS II function. (C) 2000 Elsevier Science B.V.

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Biochimica et Biophysica Acta - Bioenergetics

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