Details

Autor(en) / Beteiligte

• Christen, G
• Renger, G

Titel

The Role of Hydrogen Bonds for the Multiphasic P680+• Reduction by YZ in Photosystem II with Intact Oxyen Evolution Capacity. Analysis of Kinetic H/D Isotope Exchange Effects

Ist Teil von

• Biochemistry (Easton), 1999-02, Vol.38 (7), p.2068-2077

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

1999

Quelle

MEDLINE

Beschreibungen/Notizen

• The mechanism of multiphasic P680+• reduction by YZ has been analyzed by studying H/D isotope exchange effects on flash-induced changes of 830 nm absorption, ΔA 830(t), and normalized fluorescence yield, F(t)/F0, in dark-adapted thylakoids and PS II membrane fragments from spinach. It was found that (a) the characteristic period four oscillations of the normalized components of ΔA 830(t) relaxation and of F(t)/F0 rise in the nanosecond and microsecond time domain are significantly modified when exchangeable protons are replaced by deuterons; (b) in marked contrast to the normalized steady-state extent of the microsecond kinetics of 830 nm absorption changes which increases only slightly due to H/D exchange (about 10%) the Si state-dependent pattern exhibits marked effects that are most pronounced after the first, fourth, fifth, and eighth flashes; (c) regardless of data evaluation by different fit procedures the results lead to a consistent conclusion, that is, the relative extent of the back reaction between P680+•QA -• becomes enhanced in samples suspended in D2O; and (d) this enhancement is dependent on the Si state of the WOC and attains maximum values in S2 and S3, most likely due to a retardation of the “35 μs kinetics” of P680+• reduction. In an extension of our previous suggestion on the functional role of hydrogen bonding of YZ by a basic group X (Eckert, H.-J., and Renger, G. (1988) FEBS Lett. 236, 425−431), a model is proposed for the origin of the multiphasic P680+• reduction by YZ. Two types of different processes are involved:  (a) electron transfer in the nanosecond time domain is determined by strength and geometry of the hydrogen bond between the O−H group of YZ and acceptor X, and (b) the microsecond kinetics reflect relaxation processes of a hydrogen bond network giving rise to a shift of the equilibrium P680+•YZ ⇋ P680 toward the right side. The implications of this model are discussed.