Cystathionine is an intermediate in the synthesis of cysteine.

It is generated from homocysteine and serine by cystathionine beta synthase.

It is cleaved into cysteine and ?-ketobutyrate by cystathionine gamma-lyase.

An excess in the urine is called cystathioninuria.

Cysteine metabolism. Cystathionine beta synthase catalyzes the upper reaction and cystathionine gamma-lyase catalyzes the lower reaction.

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