**Question:** Oxidative deamination is catalyzed by -

A. Glutamate dehydrogenase
B. Alanine dehydrogenase
C. Aspartate transaminase
D. Pyruvate dehydrogenase

**Core Concept:**

Oxidative deamination is a crucial biochemical process involved in the catalysis of amino acid degradation in the citric acid cycle (Krebs cycle or Krebs cycle). In this process, the amino group of an amino acid is removed from the molecule through the action of specific enzymes.

**Why the Correct Answer is Right:**

The correct answer, **A. Glutamate dehydrogenase**, is involved in the oxidative deamination of glutamate to form α-ketoglutarate and ammonia. This process occurs within the mitochondria, where glutamate is oxidized to α-ketoglutarate by the action of glutamate dehydrogenase enzyme. This enzyme is part of the glutamate deamination pathway, which contributes to the removal of ammonia from the body and helps maintain the cellular and systemic levels of ammonia within normal limits.

**Why Each Wrong Option is Incorrect:**

**B. Alanine dehydrogenase**: Alanine dehydrogenase is involved in the reversible conversion of alanine to pyruvate, contributing to the regulation of amino acid levels in the body. Alanine dehydrogenase does not catalyze oxidative deamination.

**C. Aspartate transaminase**: Aspartate transaminase is a crucial enzyme involved in the transamination of aspartate to form α-ketoglutarate and glutamate. It does not catalyze oxidative deamination.

**D. Pyruvate dehydrogenase**: Pyruvate dehydrogenase is involved in the irreversible conversion of pyruvate to acetyl-CoA, which contributes to the production of energy in the form of ATP within the mitochondria. Pyruvate dehydrogenase does not catalyze oxidative deamination.

**Clinical Pearl:**

Oxidative deamination is a critical process in maintaining cellular and systemic ammonia levels within normal limits. The correct enzyme, glutamate dehydrogenase, plays a vital role in this process by converting glutamate to α-ketoglutarate, which contributes to the regulation of ammonia levels and the production of energy through the citric acid cycle. Understanding the role of oxidative deamination and the enzymes involved is essential for understanding the complex pathways of amino acid catabolism and maintaining cellular homeostasis.