Which enzyme is involved in the degradation of homocysteine to cysteine in the methionine cycle, and its deficiency is associated with hyperhomocysteinemia?

A Methionine synthase
B Cystathionine beta-synthase ✓
C Homocysteine methyltransferase
D Cysteine dioxygenase

Explanation

Cystathionine beta-synthase is an enzyme that catalyzes the conversion of homocysteine to cystathionine, which is then converted to cysteine. A deficiency in this enzyme leads to elevated levels of homocysteine, a condition known as hyperhomocysteinemia.

Source

NCBI Bookshelf: Homocysteine and Methionine Metabolism
Enzymes in Disease Biochemistry Amino Acid Metabolism Hard MEDICAL Confidence: high