**Core Concept**
Heme synthesis is a complex biochemical pathway that involves the coordinated action of multiple enzymes to convert succinyl-CoA and glycine into heme. The enzymes involved in heme synthesis are located in different cellular compartments, with some being found in the mitochondria and others in the cytosol.

**Why the Correct Answer is Right**
The correct answer is the enzyme that is not found in the mitochondria. The enzymes involved in heme synthesis that are found in the mitochondria include:
- **Ala synthase**: This enzyme catalyzes the condensation of succinyl-CoA and glycine to form delta-aminolevulinic acid (ALA). It is located in the mitochondria.
- **ALA dehydratase**: This enzyme catalyzes the condensation of two molecules of ALA to form porphobilinogen. Although it is often associated with the cytosol, some studies suggest that it may also be present in the mitochondria.
- **Porphobilinogen deaminase**: This enzyme catalyzes the conversion of porphobilinogen to hydroxymethylbilane. However, this enzyme is typically found in the cytosol, not the mitochondria.

**Why Each Wrong Option is Incorrect**
* **Option B:** Although ALA dehydratase is often associated with the cytosol, some studies suggest that it may also be present in the mitochondria. However, this is not the correct answer, as the question asks for the enzyme that is NOT found in the mitochondria.
* **Option C:** Porphobilinogen deaminase is typically found in the cytosol, not the mitochondria, making it the correct answer.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that heme synthesis involves a complex interplay between multiple enzymes located in different cellular compartments. Understanding the localization of these enzymes is crucial for diagnosing and managing disorders of heme synthesis, such as porphyrias.

**Correct Answer:** C. Porphobilinogen deaminase.