Step 1: Understanding the Concept:
Isozymes of hexokinase exhibit distinct tissue distributions, substrate affinities ($K_m$), and allosteric regulatory properties. Key Formula or Approach:
\[ \text{Glucose} + \text{ATP} \xrightarrow{\text{Glucokinase (Hexokinase IV)}} \text{Glucose-6-Phosphate} + \text{ADP} \] Step 2: Detailed Explanation:
Hexokinase isozyme comparison: 1. Hexokinase I--III: Present in skeletal muscle, brain, and extrahepatic tissues; have very low $K_m$ ($< 0.1\text{ mM}$, high affinity) and are allosterically inhibited by glucose-6-phosphate (G6P). 2. Glucokinase (Hexokinase IV): Expressed predominantly in the Liver (hepatocytes) and pancreatic $\beta$-cells. It has a high $K_m$ ($\approx 10\text{ mM}$, low affinity), is not inhibited by physiological G6P, and functions as a blood glucose sensor to clear postprandial glucose surges. Step 3: Final Answer:
Thus, glucokinase is present in the Liver, corresponding to option (B).
