Question

The essential co-factor in water-oxidizing process at PS II in the light reactions of photosynthesis: [Question ID = 707][Question Description = 207_34_PLB_AUG22_Q107]

• A. \(Mg^{2+}\) [Option ID = 2825]
• B. \(Mn^{2+}\) [Option ID = 2826]
• C. \(Fe^{2+}\) [Option ID = 2827]
• D. \(Cu^{2+}\) [Option ID = 2828]

Hint:

Remember the OEC as the "Manganese Center." Deficiency of Manganese significantly reduces the plant's ability to evolve oxygen during photosynthesis.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The water-oxidizing process, also known as photolysis of water, occurs in the Oxygen Evolving Complex (OEC) associated with Photosystem II. This process splits water molecules into electrons (to replace those lost by P680), protons (\(H^+\)), and molecular oxygen (\(O_2\)). The OEC requires specific metallic clusters to facilitate this 4-electron oxidation.

Step 2: Detailed Explanation:
The core of the Oxygen Evolving Complex is the Manganese-Calcium cluster (\(Mn_4CaO_5\)).
- Manganese (\(Mn\)): Manganese is unique because it can exist in several stable oxidation states (\(+2, +3, +4, +5\)). This property allows it to store positive charges as the system progresses through the "S-states" (Kok's cycle) of water oxidation. Specifically, four Mn ions work together to strip four electrons from two water molecules to produce one \(O_2\).
- Other ions like \(Cl^-\) and \(Ca^{2+}\) are also essential co-factors for the structural stability and function of the OEC.
- \(Mg^{2+}\) is the central atom of the chlorophyll ring but not the direct co-factor for water splitting.
- \(Fe^{2+}\) is found in cytochromes and FeS centers, and \(Cu^{2+}\) is found in Plastocyanin, but they do not participate in the OEC's catalytic center.

Step 3: Final Answer:
Manganese (\(Mn^{2+}\)) is the essential catalytic co-factor for the water-oxidizing process.