Enzyme connected with carboxylation of RuBP is

Options

A. Pyruvic kinase
B. Cytochrome oxidase
C. PEP carboxylase
D. RuBISCO.

Answer

**Step-by-step Solution:**

1. **Understanding the Context**: The question asks about the enzyme involved in the carboxylation of Ribulose bisphosphate (RuBP) during the process of photosynthesis, specifically in the C3 cycle (Calvin cycle).

2. **Identifying RuBP**: RuBP, or ribulose bisphosphate, is a 5-carbon compound that plays a crucial role in the first step of the Calvin cycle. It acts as a carbon dioxide acceptor.

3. **Carboxylation Process**: During the carboxylation phase, RuBP combines with carbon dioxide (CO2) to form two molecules of 3-phosphoglycerate (3-PGA). This reaction is essential for the fixation of carbon in plants.

4. **Enzyme Involved**: The enzyme that catalyzes this reaction is known as Rubisco, which stands for Ribulose bisphosphate carboxylase/oxygenase. It is the most abundant enzyme on Earth and plays a vital role in the carbon fixation process.

5. **Function of Rubisco**: Rubisco can bind to both carbon dioxide and oxygen, depending on their partial pressures in the environment. When CO2 concentration is higher, it exhibits carboxylase activity, facilitating the conversion of RuBP to 3-PGA.

6. **Conclusion**: Based on the above information, the correct answer to the question is that the enzyme connected with the carboxylation of RuBP is Rubisco.

**Final Answer**: Rubisco (Ribulose bisphosphate carboxylase/oxygenase).

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