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Cystathionine β-synthase, or the CBS enzyme that begins the transsulfuration pathway to provide sulfur groups needed for detoxification, neuroprotection by making glutathione and hydrogen sulfide, as well as for neurotransmitter and hormone modification. Sulfation can be blocked by non-steroidal anti-inflammatory drugs (e.g. aspirin), tartrazine (yellow food dye), and molybdenum deficiency.

CBS enzyme activation needs pyridoxal-5' phosphate, the active form of vitamin B6. S-adenosyl methionine regulates enzyme activity. The downstream pathway from CBS is the sulfite oxidase enzyme, made by the SUOX gene, which requires molybdenum produces sulfates from toxic sulfites. 

CBS may be upregulated to produce hydrogen sulfide if persists can counter the neuroprotective effects of hydrogen sulfide and deplete cofactors needed to make glutathione. Elevated homocysteine or cysteine may contribute to brain fog. Some CBS SNPs are associated with midline defects.

Issues in the methionine and folate cycle may contribute to the depletion of sulfur production in the transsulfuration pathway. Other subunits of transsulfuration and the sulfation pathways may be involved in neurotoxicity or neurotransmitter dysregulation.

This pathway provides a vital source of the amino acid cysteine but is also the body's only mechanism for removing sulfur-containing amino acids when present in excess. 

Regardless of which pathway homocysteine is processed through it is considered harmful when present at high levels in the blood. Excessive homocysteine can damage endothelial cells which line the circulatory system and heart, leading to inflammation and increasing the risk of coronary artery disease.

It is ideal to have Cystathionine β-synthase upregulated. B6 (pyridoxal 5-phosphate), B12 (cobalamin), B9 (folate), betaine, cysteine, serine, DHA fatty acid, EPA fatty acid, SAMe, and magnesium are known cofactors for agonist action.