Question

Name a liver specific enzyme primarily for the large domestic species and is also a zinc metalloenzyme.

• A. Glutamate dehydrogenase
• B. Aspartate transaminase
• C. Sorbitol Dehydrogenase
• D. Alkaline phosphatase

Hint:

To remember diagnostic enzymes for liver injury:
- ALT: Highly specific for dogs and cats (small animals).
- SDH (Sorbitol Dehydrogenase): Highly specific for horses, cattle, and sheep (large animals; zinc-dependent).
Because SDH is highly unstable in vitro, samples must be analyzed quickly or frozen.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Diagnostic enzymology relies on measuring serum levels of tissue-specific enzymes to identify cellular damage.
The tissue specificity of enzymes can vary significantly between small animals (dogs, cats) and large domestic animals (horses, cattle, sheep).

Step 2: Detailed Explanation:
In small animal medicine, Alanine Aminotransferase (ALT) is highly liver-specific and is used to detect hepatocellular damage.
However, in large domestic species (such as horses, cattle, and sheep), ALT activity in hepatocytes is extremely low.
Instead, other enzymes must be utilized to assess acute liver injury.
Sorbitol Dehydrogenase (SDH) (also known as L-iditol dehydrogenase) is highly liver-specific in all domestic species, particularly in large animals.
SDH is located primarily in the cytoplasm of hepatocytes.
Any acute injury causing hepatocellular necrosis leads to a rapid increase in serum SDH levels.
Furthermore, SDH is a member of the medium-chain dehydrogenase/reductase family, which are structurally characterized as zinc metalloenzymes.
Each subunit of the active homotetrameric SDH enzyme contains a tightly bound zinc ion (\(\text{Zn}^{2+}\)) that is essential for its catalytic activity.
While Glutamate dehydrogenase (GDH) (A) is also highly liver-specific in large animals, it is a mitochondrial enzyme and is not typically defined primarily by its zinc-metalloenzyme characteristics in this diagnostic context.
Aspartate transaminase (AST) (B) and Alkaline phosphatase (ALP) (D) are not liver-specific.

Step 3: Final Answer:
The liver-specific zinc metalloenzyme used primarily in large domestic species is Sorbitol Dehydrogenase.