**Core Concept:** Glycolysis is the process of breaking down glucose into pyruvate, producing energy in the form of ATP, and generating reducing agents (nicotinamide adenine dinucleotide [NADH] and flavin adenine dinucleotide [FAD]). It occurs in the cytoplasm of cells and is the primary source of ATP production in anaerobic conditions. The first committed step is the irreversible conversion of glucose to glucose-6-phosphate.

**Why the Correct Answer is Right:** The correct answer, **Option C: Phosphoglucoisomerase**, is the enzyme responsible for catalyzing the first committed step in glycolysis. This enzyme converts glucose to glucose-6-phosphate.

**Why Each Wrong Option is Incorrect:**

**A.** **Aldolase (ALDO)** catalyzes the second step in glycolysis, where fructose-6-phosphate is cleaved into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.

**B.** **Pyruvate kinase (PK)** is involved in the final step of glycolysis, converting phosphoenolpyruvate to pyruvate.

**D.** **Enolase (ENO)** catalyzes the conversion of 2-phosphoglycerate to phosphoenolpyruvate, which is the third step in glycolysis.

**Clinical Pearl:** The knowledge of glycolysis and its key enzymes is essential for understanding cellular energy production and the differential diagnosis of various pathologies, such as impaired glucose tolerance and diabetes mellitus, where glucose homeostasis is disrupted.

**Correct Answer:** **Phosphoglucoisomerase (PGM)** is the correct answer. Phosphoglucoisomerase is involved in the reversible interconversion between glucose-6-phosphate and fructose-6-phosphate. This enzyme is crucial for maintaining the balance between glycolysis and gluconeogenesis pathways and is essential for cellular energy production and glucose homeostasis.