Which of the following enzymes must all gluconeogenic tissues express in order to carry out gluconeogenesis?

• A. Pyruvate kinase
• B. Hexokinase
• C. Phosphofructokinase-1 (PFK-1)
• D. Glucose-6-phosphatase

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the process of gluconeogenesis. Gluconeogenesis is the metabolic pathway that generates glucose from non-carbohydrate precursors, such as lactate, glycerol, and amino acids. It primarily occurs in the liver and kidneys.
2. Step 2: Identify the enzymes involved in gluconeogenesis. Gluconeogenesis bypasses the irreversible steps of glycolysis by using specific enzymes. These include pyruvate carboxylase, phosphoenolpyruvate carboxykinase (PEPCK), fructose-1,6-bisphosphatase, and glucose-6-phosphatase.
3. Step 3: Recognize the role of glucose-6-phosphatase. This enzyme is essential for the final step of gluconeogenesis, where glucose-6-phosphate is converted into free glucose. This step is crucial for exporting glucose into the bloodstream, especially in the liver and kidneys.
4. Step 4: Compare the listed enzymes. Pyruvate kinase, hexokinase, and phosphofructokinase-1 (PFK-1) are glycolytic enzymes that function in glucose breakdown, not synthesis. These enzymes are not involved in gluconeogenesis and are not required for this pathway.
5. Step 5: Conclude that glucose-6-phosphatase is the correct answer. It is the enzyme that all gluconeogenic tissues must express to complete gluconeogenesis and release glucose into the bloodstream.