The product formed by malic dehydrogenase is

Options

A. Malic acid
B. Fumaric acid
C. Oxaloacetic acid
D. Succinic acid

Answer

To determine the product formed by malic dehydrogenase, we can follow these steps:

### Step 1: Understand the Role of Malic Dehydrogenase
Malic dehydrogenase, also known as malate dehydrogenase, is an enzyme that plays a crucial role in the Krebs cycle (also known as the citric acid cycle or TCA cycle).

**Hint:** Remember that enzymes are biological catalysts that facilitate specific biochemical reactions.

### Step 2: Identify the Substrate
The substrate for malic dehydrogenase is malic acid (or malate). This is the compound that the enzyme acts upon.

**Hint:** In biochemical reactions, the substrate is the starting material that is transformed by the enzyme.

### Step 3: Determine the Reaction
The reaction catalyzed by malic dehydrogenase converts malic acid (malate) into oxaloacetic acid (oxaloacetate). During this reaction, a reducing equivalent (NADH) is produced.

**Hint:** Look for the products of the reaction in the context of the Krebs cycle, where malate is converted to oxaloacetate.

### Step 4: Analyze the Options
Now, let's analyze the options provided:
- **Malic acid:** This is the substrate, not the product.
- **Fumaric acid:** This is an intermediate in the Krebs cycle but is not produced by malic dehydrogenase.
- **Oxaloacetic acid:** This is the correct product formed by the action of malic dehydrogenase.
- **Succinic acid:** This is another intermediate in the Krebs cycle but is not produced by this enzyme.

**Hint:** Eliminate options that are substrates or intermediates not directly produced by the enzyme in question.

### Step 5: Conclusion
The product formed by malic dehydrogenase is **oxaloacetic acid**.

**Final Answer:** Oxaloacetic acid (Option C).