**Core Concept**
Aminopeptidase is a type of enzyme involved in the breakdown of peptides. It is a metalloprotease that cleaves amino acids from the N-terminus of peptides. This enzyme plays a crucial role in various physiological processes, including protein digestion and regulation of blood pressure.

**Why the Correct Answer is Right**
Aminopeptidase is primarily found in the brush border of the small intestine, where it helps to digest dietary proteins. The enzyme uses zinc ions as cofactors to cleave the N-terminal amino acid from peptides. This process is essential for the absorption of amino acids in the gut. Additionally, aminopeptidase is also present in other tissues, such as the kidneys and brain, where it regulates the levels of various peptides.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because aminopeptidase is not primarily associated with the liver. While the liver does contain various enzymes involved in protein metabolism, aminopeptidase is specifically found in the small intestine and other tissues.
* **Option B:** This option is incorrect because carboxypeptidase is a different type of enzyme that cleaves amino acids from the C-terminus of peptides, not the N-terminus.
* **Option C:** This option is incorrect because peptidase is a general term that refers to any enzyme involved in peptide breakdown. Aminopeptidase is a specific type of peptidase that cleaves amino acids from the N-terminus of peptides.

**Clinical Pearl / High-Yield Fact**
Aminopeptidase inhibitors, such as bestatin, have been used to treat certain types of cancer by inhibiting the breakdown of peptides involved in tumor growth.

**Correct Answer:** D.