Case Scenario: A 65-year-old male presents with fatigue, paresthesia (numbness and tingling in hands and feet), and memory impairment. Blood tests reveal elevated homocysteine levels and macrocytosis. His physician suspects a vitamin B12 deficiency affecting methyl group transfer in amino acid metabolism. Which of the following enzymes requires cobalt-containing vitamin B12 to facilitate the conversion of homocysteine to methionine?
