Out of the following, which is the rate limiting enzyme in glycolysis?

Options

A. Pyruvate kinase
B. Phosphofructo kinase
C. Phosphoglucoisomerase
D. Gluco kinase

Answer

**Step-by-Step Solution:**

1. **Understanding Glycolysis**: Glycolysis is a metabolic pathway that converts glucose into pyruvate through a series of enzymatic reactions. It consists of ten steps and occurs in the cytoplasm of the cell.

2. **Identifying the Substrate**: The substrate for glycolysis is glucose, which undergoes a series of transformations to ultimately produce two molecules of pyruvate.

3. **Phases of Glycolysis**: Glycolysis can be divided into two phases:
- **Preparatory Phase**: The first half of glycolysis where energy (ATP) is consumed to convert glucose into fructose 1,6-bisphosphate.
- **Payoff Phase**: The second half where ATP and NADH are produced.

4. **Key Steps in the Preparatory Phase**:
- Glucose is phosphorylated to form glucose 6-phosphate, using 1 ATP.
- Glucose 6-phosphate is isomerized to fructose 6-phosphate.
- Fructose 6-phosphate is then phosphorylated to form fructose 1,6-bisphosphate, using another ATP.

5. **Identifying the Rate Limiting Step**: The rate limiting step in glycolysis is the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate. This step is crucial as it is heavily regulated and determines the overall rate of glycolysis.

6. **Enzyme Involved**: The enzyme that catalyzes this rate limiting step is **phosphofructokinase (PFK)**. This enzyme is key in regulating the flow of carbon through the glycolytic pathway.

7. **Conclusion**: Based on the above analysis, the rate limiting enzyme in glycolysis is phosphofructokinase.

**Final Answer**: The rate limiting enzyme in glycolysis is **phosphofructokinase**.

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