Manganese complexes proteins

In photosynthesis, water oxidation is accomplished by photosystem II (PSII), which is a large membrane-bound protein complex (158-161). To the central core proteins D1 and D2 are attached different cofactors, including a redox-active tyro-syl residue, tyrosine Z (Yz) (158-162), which is associated with a tetranuclear manganese complex (163). These components constitute the water oxidizing complex (WOC), the site in which the oxidation of water to molecular oxygen occurs (159, 160, 164). The organization is schematically shown in Fig. 18. 

At variance with the aqua ion, in most manganese(II) proteins and complexes the contact contribution to relaxation is found negligible. This is clearly the case for MnEDTA (Fig. 33), the relaxivity of which indicates the presence of the dipolar contribution only, and one water molecule bound to the complex 93). Actually the profile is very similar to that of GdDTPA (see Chapter 4), and is provided by the sum of inner-sphere and outer-sphere contributions of the same order. The relaxation rate of MnDTPA is accounted for by outer-sphere relaxation only (see Section II.A.7), no water molecules being coordinated to the complex 94). 

OXII is responsible for the production of molecular oxygen in photosynthesis. A manganese complex, probably with four atoms of manganese, is attached to a protein molecule. It reduces OXjj which is recycled for use by another excited chlorophyll molecule in PS-II. In the redox reaction the manganese shuttles between two oxidation states with each manganese atom... 

Iodolabeling studies on photosystem II particles from higher plants and cyanobacteria (221) and on a PSII complex (227) specifically labeled the herbicide-binding protein. As 1 is believed to donate electrons to Z, the secondary electron donor which is believed to accept electrons from the photosynthetic manganese complex, these experiments indicate a role for this protein on the oxidizing side of PSII. Consequently, Z must at least be located near, if not in, the herbicidebinding polypeptide (222). 

As 2 electrons move from each water molecule to NADP1 (blue arrows), about two H+ are pumped from the stroma into the thylakoid lumen. Two additional H+ are generated within the lumen by the oxygen-evolving complex. The flow of protons through the proton pore in CF0 drives the synthesis of ATP in CF (MSP = manganese stabilizing protein ph = pheophytin Fd = ferredoxin FNR = ferredoxin-NADP oxidoreductase)... 

The calcium and barium salts have been used for the oxidation of complex proteins. The calcium salt has the advantage in that it forms insoluble products. The calcium oxide combines with the manganese dioxide to form the insoluble CaO Mn02, thus simplifying recovery of products. y Alkaline Solution. When potassium permanganate alone is used in aqueous solution, the solution becomes alkaline through the formation potassium hydroxide ... 

---