Question

Hexokinase isozymes are affected differently by their product. Which of the two isozymes, hexokinase II or hexokinase IV, reaches Vmax/2 at lower substrate concentration? (2 points) Why does this make sense physiologically? (2 points) How does [ATP] affect the activity of these isozymes? (2 points)

Answer 1

Hexokinase II reaches Vmax/2 at lower conc. than hexokinase IV.

Hexokinase II is lower Km value than hexokinase IV thus hecokinase II has high affinity for substate and it's reaches to maximum velocity or rate of reaction at low conc of glucose as compared to hexokinase IV.

This make sense physilogically as low affinity of hexokinase IV present at liver as it storage house of glucose so when excess amount of glucose present then here glycolysis start as Km is high which means low affinity.

While hecokinase II will present in blood or RBC which purely depends on glucose for its Energy so here even low conc of glucose will be utilizes for glycolysis process to generate ATP as Km is low which means high affinity.

Thanks..!