AIIMS CRE, SNO-2024: Which enzyme converts Glucose-6-phosphate to 6-phosphogluconolactone?

AIIMS CRE, SNO-2024

Biochemistry & Nutrition

Easy

Appeared in: AIIMS CRE, SNO-2024

Explanation

G6PD (Glucose-6-phosphate dehydrogenase) is the enzyme that catalyzes the conversion of glucose-6-phosphate to 6-phosphogluconolactone.
This is the first and rate-limiting step of the Pentose Phosphate Pathway (PPP), also known as the hexose monophosphate shunt.
This reaction is crucial as it reduces NADP+ to NADPH.
NADPH is a vital molecule that protects cells, particularly red blood cells, from oxidative damage by regenerating reduced glutathione.

Option A: Hexokinase is the enzyme that catalyzes the first step of glycolysis, converting glucose into glucose-6-phosphate. It does not act on glucose-6-phosphate to form 6-phosphogluconolactone.
Option C: Phosphofructokinase (PFK) is a key regulatory enzyme in glycolysis that converts fructose-6-phosphate into fructose-1,6-bisphosphate. It acts on a different substrate and in a different pathway.
Option D: Enolase is an enzyme that functions late in the glycolytic pathway. It catalyzes the dehydration of 2-phosphoglycerate to form phosphoenolpyruvate.

Visual 1: Diagram: A flowchart of the Pentose Phosphate Pathway, highlighting the initial step where G6PD converts Glucose-6-phosphate to 6-phosphogluconolactone and produces NADPH.
Visual 2: Diagram: A flowchart of the Glycolysis pathway, showing the distinct roles and positions of Hexokinase, Phosphofructokinase, and Enolase.

Clinical Relevance

Nursing practice connection: Knowing Enzymatic reaction in the Pentose Phosphate Pathway helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding the role of G6PD is critical for nurses due to G6PD deficiency, a common genetic condition. Lack of this enzyme leads to a decreased supply of NADPH, making red blood cells susceptible to hemolysis from oxidative stress.
Nurses must be aware of common triggers for hemolysis in G6PD-deficient patients, such as certain medications (e.g., sulfonamides, antimalarials like primaquine), infections, and foods like fava beans. Patient education on avoiding these triggers is a key nursing responsibility.
What if? If a patient with undiagnosed G6PD deficiency is admitted with a severe infection, the nurse should be vigilant for signs of hemolytic anemia (jaundice, dark urine, fatigue, tachycardia) as infection itself is a major oxidative stressor that can trigger a crisis.

How to Approach the Question

First, identify the core of the question. It is a factual recall question asking for a specific enzyme that catalyzes a specific biochemical reaction.
Analyze the substrate (Glucose-6-phosphate) and the product (6-phosphogluconolactone) mentioned in the question.
Recall the major pathways of carbohydrate metabolism. This particular reaction is the entry point and rate-limiting step of the Pentose Phosphate Pathway (PPP).
Identify the enzyme responsible for this step, which is Glucose-6-phosphate dehydrogenase (G6PD).
Evaluate the other options to confirm the answer. Hexokinase, Phosphofructokinase, and Enolase are all key enzymes in the glycolysis pathway, not the PPP. This confirms that G6PD is the correct choice.

Concept Tested & Keywords

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Textbook of Biochemistry for Medical Students 6th Edition — DM Vasudevan p. 241-249