UV‐spectral characterization in Tris‐washed chloroplasts of the redox component D₁ which functionally connects the reaction center with the water‐oxidizing enzyme system Y in photosynthesis

Abstract

Amplitude and relaxation kinetics of UV-absorption changes induced in Tris-washed chloroplasts by the second flash of repetitive double flash groups were found to be dependent on the time between the flashes of each group. An analysis of these data leads to the conclusion that after oxidation by P680+ the donor component, Dy , becomes mainly reduced by the primary (QA) and secondary (Qi) plastoquinone in non-B-type and B-type system II centers, respectively. Dp reduction with QA occurs with tl/ = 60-100 ms, and D$ reduction with QB is biphasic with half-times of 0.1-0.5 and S-10 s. The difference spectrum of the oxidized vs reduced form of D1 is presented in the range 250-370nm. It is characterized by positive bands peaking at 265-270 and 300-305 nm with a smaller band around 350 nm; negative bands are not observed. Photosystem II Tris-washing Redox equivalent recombination Donor component DI UV-difference spectrum Dy/D,

The Metal Centers of the Photosynthetic Oxygen‐evolving Complex *

“…Moreover, the absorbance changes are not unlike those reported for the difference spectrum for an earlier donor, Z+/Z. measured in Tris-washed chloroplasts (Weiss and Renger, 1984) and in other PS-I1 preparations (Diner and de Vitry. 1984;Dekker et al, 1984), and for photoreduction of QA, suggesting the possibility of spectral interference.…”

Absorption changes of Photosystem II donors and acceptors in algal cells

“…A slightly different spectrum was also reported recently [17]. The UV part of the spectra reported by these authors resembles that of a semiquinone cation, such as that of 2,3-dimethyl-l ,Cnaphthoquinone 1161, or of duroquinone 1121.…”

Two sites of photoinhibition of the electron transfer in oxygen evolving and Tris-treated PS II membrane fragments from spinach

“…The much higher susceptibility of PS II membrane fragments with selectively inhibited O2-evolution and its partial protection afforded by artificial electron donors (Cleland et al 1987, Theg et al 1986, Callahan et al 1986 of this study) supports the idea that photoinhibition at site II is predominantly due to an oxidation of nearby pigment-or protein components by highly oxidizing radicals (like P680 ÷ or Yz x) or by a modification of Yz itself. This oxidative degradation leads to a functional disconnection of P680 from Yz-In this respect it is interesting to note that the increase of the quantum yield of photoinhibition at site II by a factor of 1000 upon elimination of the O2-evolution capacity corresponds surprisingly well with the retardation of the steady state lifetime of Yz x upon Tris-washing (from several hundred/~s to a few hundred milliseconds, see Babcock and Sauer 1975a, Babcock et al 1976, Dekker et al 1984, Weiss and Renger 1984, Renger and Weiss 1986.…”