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Homocysteine desulfhydrase

The enzyme homocysteine desulfhydrase (EC 4.4.1.2) catalyzes the chemical reaction

L-homocysteine + H<sub>2</sub>O = hydrogen sulfide + NH<sub>3</sub> + 2-oxobutanoate (overall reaction)
:(1a) <small>L</small>-homocysteine = hydrogen sulfide + 2-aminobut-2-enoate
:(1b) 2-aminobut-2-enoate = 2-iminobutanoate (spontaneous)
:(1c) 2-iminobutanoate + H<sub>2</sub>O = 2-oxobutanoate + NH<sub>3</sub> (spontaneous)

This enzyme belongs to the family of lyases, specifically the class of carbon-sulfur lyases. The systematic name of this enzyme class is <small>L</small>-homocysteine hydrogen-sulfide-lyase (deaminating; 2-oxobutanoate-forming). Other names in common use include homocysteine desulfurase, <small>L</small>-homocysteine hydrogen-sulfide-lyase (deaminating). This enzyme participates in nitrogen and sulfur metabolism. It employs one cofactor, pyridoxal phosphate.

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