This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Activity of which of the following enzyme is NOT affected by insulin: 
Select and explain. 
A. Pyruvate kinase, B. Glycogen synthase, C. Hexokinase, D. Glucokinase
C: Hexokinase
Answer: C: Hexokinase 
Explanation: Hexokinase

Transfer Phosphate group from ATP to Glucose.
Has high affinity for glucose (Or Lower Km) and not affected by insulin.
Mg2+ is the cofactor.
Irreversible step.
ATP is utilized.

Glucokinase

Present in Liver and Pancreatic β cells.
Has low affinity for Glucose. (High Km).
Hence acts only when blood glucose is very high  (> 100 mg/dl).
Induced by Insulin following a meal.
Play  an  important  role  in  regulation  of  blood glucose.
In the liver, function of Glucokinase is to remove glucose from portal vein following a meal
In the beta cells of Pancreas, function of Glucokinase is to release Insulin. 

Glycogen Synthase
Insulin favor Glycogenesis by dephosphorylating, Glycogen Synthase.
Key concept: