___________produced by bacterium Streptococcus and modified by genetic engineering is used as a clot buster for removing clots from the blood vessels of patients who have undergone myocardial infarction leading to heart attack.

Options

A. Lipase
B. Streptokinase
C. Cyclosporin A
D. Antibiotic streptomycin

Explanation

**Step-by-Step Solution:**

1. **Identify the Bacterium**: The question states that the substance is produced by the bacterium *Streptococcus*. This is the first clue that helps narrow down the options.

2. **Understand the Function**: The substance is described as a "clot buster," which means it is used to dissolve blood clots. This is particularly important in medical emergencies such as myocardial infarction (heart attack).

3. **Consider Genetic Engineering**: The question mentions that the substance has been modified by genetic engineering. This indicates that the original product from the bacterium has been altered to enhance its effectiveness or usability.

4. **Evaluate the Options**: The options provided are:
- Lipase
- Streptokinase
- Cyclosporine A
- Antibiotic Streptomycin

5. **Analyze Each Option**:
- **Lipase**: This enzyme is used for breaking down fats and is not related to clot busting. It is typically derived from fungi, not *Streptococcus*.
- **Streptokinase**: This is an enzyme produced by *Streptococcus* that acts as a clot buster. It is indeed modified by genetic engineering for medical use.
- **Cyclosporine A**: This is an immunosuppressive drug obtained from fungi, specifically *Trichoderma*, and is not related to clot busting.
- **Antibiotic Streptomycin**: This antibiotic is produced by *Streptomyces*, a different genus of bacteria, and is not involved in clot busting.

6. **Conclude the Correct Answer**: Based on the analysis, the correct answer is **Streptokinase**, as it is the only option that meets all the criteria mentioned in the question.

**Final Answer**: Streptokinase

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