Copper was added to truncated, recombinant cystathionine beta-synthase (CBS), and the enzyme activity was assessed by measuring the production of cystathionine. 10 microM copper significantly decreased CBS activity by 50% while 25 microM copper decreased CBS activity by 70%. This inhibition was negated when an analog of the N-terminus of human albumin, Asp-Ala-His-Lys (DAHK), a strong transition metal binding peptide, was added. The use of copper chelators could significantly reduce in vivo homocysteine levels.