In which of the following substrate level phosphorylation does not occur ?

Options

A. 1, 3-biphosphoglyceric acid `rarr` 3 phosphoglyceric acid
B. Glucose 6-phosphate `rarr` Fructose 6-phosphate
C. Succinyl CoA `rarr` Succinic acid
D. Phosphoenol pyruvic acid `rarr` pyruvic acid.

Answer

To determine in which of the given reactions substrate-level phosphorylation does not occur, we need to analyze each option based on the definition of substrate-level phosphorylation. This process involves the direct transfer of a phosphate group to ADP to form ATP, typically catalyzed by enzymes known as kinases.

### Step-by-Step Solution:

1. **Understand Substrate-Level Phosphorylation**:
- Substrate-level phosphorylation is the process of adding a phosphate group to ADP to form ATP, occurring in metabolic pathways like glycolysis and the citric acid cycle.

2. **Analyze Each Option**:
- **Option 1**: Conversion of 1,3-bisphosphoglyceric acid to 3-phosphoglyceric acid.
- In this reaction, ADP is phosphorylated to ATP. Therefore, substrate-level phosphorylation occurs here.

- **Option 2**: Conversion of glucose 6-phosphate to fructose 6-phosphate.
- This reaction does not involve the addition of a phosphate group; it is an isomerization reaction. Therefore, substrate-level phosphorylation does not occur here.

- **Option 3**: Conversion of succinyl CoA to succinic acid.
- In this reaction, GTP or ATP is produced from GDP or ADP, indicating that substrate-level phosphorylation occurs.

- **Option 4**: Conversion of phosphoenolpyruvic acid to pyruvic acid.
- In this reaction, AMP is converted to ATP, indicating that substrate-level phosphorylation occurs.

3. **Conclusion**:
- After analyzing all options, the reaction in which substrate-level phosphorylation does not occur is the conversion of glucose 6-phosphate to fructose 6-phosphate.

### Final Answer:
The reaction in which substrate-level phosphorylation does not occur is the conversion of glucose 6-phosphate to fructose 6-phosphate.