Hi, Homocysteine can be broken down only via the trans-sulfuration pathway which required P5P (via B6) and serine. Make sure you have both on-board. This catabolic route allows the elimination of L-methionine and the toxic metabolite L-homocysteine (PubMed:23981774, PubMed:20506325, PubMed:23974653).
CSB is also structurally heme dependent (a heme sensor protein). “Cystathionine beta-synthase (CBS) is a unique heme-containing enzyme that catalyzes a pyridoxal 5′-phosphate (PLP)-dependent condensation of serine and homocysteine to give cystathionine. Deficiency of CBS leads to homocystinuria, an inherited disease of sulfur metabolism characterized by increased levels of the toxic metabolite homocysteine. Here we present the X-ray crystal structure of a truncated form of the enzyme. CBS shares the same fold with O-acetylserine sulfhydrylase but it contains an additional N-terminal heme binding site. This heme binding motif together with a spatially adjacent oxidoreductase active site motif could explain the regulation of its enzyme activity by redox changes.”
