Activity of which of the following enzyme is NOT affected by insulin:: (A) Pyruvate kinase, (B) Glycogen synthase, (C) Hexokinase, (D) Glucokinase
Answer is C. 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: