## **Core Concept**
The question tests understanding of glucose metabolism, specifically postprandial (after meal) glucose utilization. This process involves various enzymes that facilitate the uptake and utilization of glucose by cells. The key enzyme in this context is involved in glycolysis, the pathway by which glucose is converted into energy.

## **Why the Correct Answer is Right**
The correct answer, **Glucokinase**, plays a crucial role in the liver for postprandial glucose utilization. After a meal, blood glucose levels rise, triggering insulin release. Glucokinase is induced by insulin and facilitates the phosphorylation of glucose to glucose-6-phosphate in the liver, a critical step for glucose storage as glycogen or further metabolism through glycolysis. This enzyme has a high Km for glucose, meaning it is active when glucose levels are high, making it ideal for postprandial glucose metabolism.

## **Why Each Wrong Option is Incorrect**
- **Option A: Hexokinase** - While hexokinase also phosphorylates glucose to glucose-6-phosphate, it has a low Km for glucose and is not as specifically induced by insulin for postprandial glucose utilization. It is more ubiquitous and involved in basal glucose uptake.
- **Option B: Glucose-6-phosphatase** - This enzyme is involved in gluconeogenesis and glycogenolysis, catalyzing the conversion of glucose-6-phosphate to glucose for release into the bloodstream, the opposite of what is asked.
- **Option D: Pyruvate Kinase** - This enzyme is indeed involved in glycolysis but acts later in the pathway, converting phosphoenolpyruvate (PEP) into pyruvate. It is not the primary enzyme for initiating glucose utilization postprandially.

## **Clinical Pearl / High-Yield Fact**
A key clinical correlation is that **glucokinase** mutations can lead to maturity-onset diabetes of the young (MODY), a form of diabetes characterized by an autosomal dominant inheritance pattern and often presents at a young age. This highlights the enzyme's critical role in glucose metabolism and its impact on disease when dysfunctional.

## **Correct Answer:** . Glucokinase