**Core Concept**
KF ring, also known as Kayser-Fleischer ring, is a clinical sign associated with Wilson's disease, an autosomal recessive disorder characterized by excessive accumulation of copper in the body. The deposition of copper in the Descemet's membrane of the cornea leads to the formation of this characteristic ring.

**Why the Correct Answer is Right**
The correct answer is a protein called _ceruloplasmin_. Ceruloplasmin is a copper-carrying protein that plays a crucial role in the transport and metabolism of copper in the body. In Wilson's disease, mutations in the ATP7B gene lead to impaired ceruloplasmin function, resulting in the accumulation of toxic levels of copper in the body. The excess copper is then deposited in the Descemet's membrane of the cornea, forming the Kayser-Fleischer ring.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a protein related to copper metabolism.
**Option B:** This option is incorrect because it does not accurately describe the pathophysiology of Wilson's disease.
**Option C:** This option is incorrect because it is not directly related to the formation of the Kayser-Fleischer ring.

**Clinical Pearl / High-Yield Fact**
The Kayser-Fleischer ring is a hallmark sign of Wilson's disease, and its presence is a critical diagnostic clue. In addition to the Kayser-Fleischer ring, other clinical features of Wilson's disease include liver disease, neurological symptoms, and psychiatric problems.

**Correct Answer: D. Ceruloplasmin**