GENERATION, OXIDATION BY THE OXIDIZED FORM OF THE TYROSINE OF POLYPEPTIDE D2, AND POSSIBLE ELECTRONIC CONFIGURATION OF THE REDOX STATE-S(0), STATE-S-1, AND STATE-S-2 OF THE WATER OXIDASE IN ISOLATED SPINACH THYLAKOIDS
J. Messinger et G. Renger, GENERATION, OXIDATION BY THE OXIDIZED FORM OF THE TYROSINE OF POLYPEPTIDE D2, AND POSSIBLE ELECTRONIC CONFIGURATION OF THE REDOX STATE-S(0), STATE-S-1, AND STATE-S-2 OF THE WATER OXIDASE IN ISOLATED SPINACH THYLAKOIDS, Biochemistry, 32(36), 1993, pp. 9379-9386
Suitable treatment of thylakoids with hydrazine permits a high populat
ion of the redox states S0, S-1, and S-2 in the water oxidase. Experim
ents performed with dark-adapted samples enriched either in the oxidiz
ed or reduced form of the redox-active tyrosine, Y(D), of PolYpeptide
D2 reveal that Y(D)ox is a unique endogenous oxidant within the PS II
complex which causes a one-electron abstraction from the water oxidase
in states S0, S-1, and S-2, respectively. A kinetic analysis of the p
eriod four oscillation of oxygen yield induced by a train of short fla
shes in dark-adapted samples permits the determination of the rate con
stants of electron abstraction from the reduced water oxidase by Y(D)o
x. A value of 9 x 10(-4) s-1 was found for the oxidation of S0 and S-2
, while S-1 becomes oxidized with a rate constant of 4 x 10(-4) s-1 at
20-degrees-C and pH 7.2. The redox state S0 generated either from S1
via the three-flash-induced oxidative pathway through S4 or from a one
-flash oxidation of the S-1 state obtained by S1 reduction with NH2NH2
exhibits the same kinetics as S0 oxidation by Y(D)ox. On the basis of
these findings and data taken from the literature, the electronic con
figuration of the Manganese atoms in the tetranuclear cluster is discu
ssed. It is assumed that the dimer model of two binuclear manganese gr
oups within the tetranuclear cluster comprises a functional heterogene
ity: (i) one binuclear center, referred to as the catalytic group, is
proposed to be involved in the oxidative pathway leading to the eventu
al oxidation of water to dioxygen, and (ii) the other binuclear center
, symbolized as component C, is redox-inert during the oxidative pathw
ay but can be reduced by exogenous (and endogenous?) components, there
by forming the states S-1 and S-2 Of the water oxidase. An asymmetric
protein matrix around the tetranuclear manganese cluster is assumed to
be responsible for the functional heterogeneity of the manganese cent
ers.