Which enzyme is responsible for the conversion of methionine to homocysteine in the methionine cycle, and its deficiency is associated with hyperhomocysteinemia?

A Methionine synthase
B S-adenosylhomocysteine hydrolase
C Cystathionine beta-synthase ✓
D S-adenosylmethionine decarboxylase

Explanation

Cystathionine beta-synthase catalyzes the conversion of homocysteine and serine to cystathionine. Its deficiency leads to hyperhomocysteinemia, which is a risk factor for cardiovascular diseases.

Source

Scriver's The Metabolic and Molecular Bases of Inherited Disease
Enzymes in Disease Biochemistry Amino Acid Metabolism Medium MEDICAL Confidence: medium