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A structural model for the photosynthetic oxygen evolving manganese cluster
MANGANESE
G002
363
A S T R U C T U R A L M O D E L F O R THE P H O T O S Y N T H E T I C OXYGEN E V O L V I N G MANGANESE CLUSTER
Melvin P, Klein, Vittal K. Yachandra, Victoria J. DeRose, Ishita Mukerji, Matthew J. Latimer, and Kenneth Sauer
Melvin Calvin Laboratory, Chemical Biodynamics Division, Lawrence Berkeley Laboratory and Department of Chemistry, University of California, Berkeley, CA 94720 The photosynthetic oxidation of water to form molecular oxygen in cyanobacteria and higher plants is catalyzed by a cluster of four Mn atoms. Extensive studies have shown that C1- and Ca +2 are essential cofactors involved in this water oxidation reaction [1]. Recent EXAFS results on oxygen evolving preparations from both spinach and cyanobacteria show three distinct Fourier peaks which can be modelled as interactions from bridging and terminal ligand atoms (O, N), Mn at 2.7 /~, and Mn and/or Ca at 3.3 A. The 2.7 A vector shows moderate dichroism in oriented samples, whereas the 3.3 /~ vector is oriented perpendicular to the plane of the membrane. The amplitude of the :3.3 ]k peak increases dramatically upon replacement with Sr. The results from studies with bromide-replaced samples rule out a bridging halide ligand but allow for a single halide ligand to the Mn. Electron spin echo envelope modulation studies of 14N and 15N-labelled samples indicate hyperfine coupling between N and the spin on the Mn which gives rise to the multiline EPR signal present in the $2 state [2]. A model consistent with our current results is shown below.
T
Histidinel
IMembrane1 I Normal
0 0
(E)c~ @ca
1. (a) G.T. Babcock, In New Comprehensive Biochemistry, vol. 15. Photosynthesis: J. Amesz, Ed.; Elsevier: Amsterdam (1987). (b) R.J. Debus, Biochim. Biophys. Acta (1991) (submitted). 2. VJ. DeRose, V.K. Yachandra, A.E. McDermott, R.D. Britt, K.Sauer and 1VI.P. Klein, Biochemistry, 30, 1335 (1991).
G002
363
A S T R U C T U R A L M O D E L F O R THE P H O T O S Y N T H E T I C OXYGEN E V O L V I N G MANGANESE CLUSTER
Melvin P, Klein, Vittal K. Yachandra, Victoria J. DeRose, Ishita Mukerji, Matthew J. Latimer, and Kenneth Sauer
Melvin Calvin Laboratory, Chemical Biodynamics Division, Lawrence Berkeley Laboratory and Department of Chemistry, University of California, Berkeley, CA 94720 The photosynthetic oxidation of water to form molecular oxygen in cyanobacteria and higher plants is catalyzed by a cluster of four Mn atoms. Extensive studies have shown that C1- and Ca +2 are essential cofactors involved in this water oxidation reaction [1]. Recent EXAFS results on oxygen evolving preparations from both spinach and cyanobacteria show three distinct Fourier peaks which can be modelled as interactions from bridging and terminal ligand atoms (O, N), Mn at 2.7 /~, and Mn and/or Ca at 3.3 A. The 2.7 A vector shows moderate dichroism in oriented samples, whereas the 3.3 /~ vector is oriented perpendicular to the plane of the membrane. The amplitude of the :3.3 ]k peak increases dramatically upon replacement with Sr. The results from studies with bromide-replaced samples rule out a bridging halide ligand but allow for a single halide ligand to the Mn. Electron spin echo envelope modulation studies of 14N and 15N-labelled samples indicate hyperfine coupling between N and the spin on the Mn which gives rise to the multiline EPR signal present in the $2 state [2]. A model consistent with our current results is shown below.
T
Histidinel
IMembrane1 I Normal
0 0
(E)c~ @ca
1. (a) G.T. Babcock, In New Comprehensive Biochemistry, vol. 15. Photosynthesis: J. Amesz, Ed.; Elsevier: Amsterdam (1987). (b) R.J. Debus, Biochim. Biophys. Acta (1991) (submitted). 2. VJ. DeRose, V.K. Yachandra, A.E. McDermott, R.D. Britt, K.Sauer and 1VI.P. Klein, Biochemistry, 30, 1335 (1991).