Question

Which reactions of phase I and phase II metabolism require energy, and where does this energy come from (in what molecular form)?

Answer 1

Conjugation reactions of Phase II metabolism require high energy.

Phase II metabolism includes glucuronide conjugation, acetylation, methylation,sulfate conjugation,glycine conjugation, glutathione conjugation etc.

In conjugation reactions energy is required mainly for the synthesis of cofactors needed for conjugation reactions.

In glucuronide conjugation,the glucuronic acid present in the UDP glucuronic acid is transferred to a substrate with the help of the enzyme UDP glucuronyl transferase.It is an energy consuming reaction,which requires UTP for the synthesis of UDP glucuronic acid and UDP glucose.If glycogen acts as source of carbohydrate UTP is required,if glucose acts as source of carbohydrate ATP is required so that Glucose can be converted into Glucose 1 phosphate which in combination with UTP gives rise to UDP glucose.

The source of energy is from glucose and glycogen in the form of UTP and ATP.