Cystathionine hydrolysis

This enzyme [EC 4.4.1.6] catalyzes the pyridoxal-phos-phate-dependent hydrolysis of an 5-alkyl-L-cysteine to generate an alkyl thiol, ammonia, and pyruvate. The reaction is an a,/3-elimination. In yeast, the enzyme may be identical to cystathionine /3-lyase. See also Alliin Lyase... 

This pyridoxal-phosphate-dependent enzyme [EC 4.4.1.8], also referred to as /3-cystathionase and cystine lyase, catalyzes the hydrolysis of cystathionine to yield homocysteine, pyruvate, and ammonia. 

Beta replacement is catalyzed by such enzymes of amino acid biosynthesis as tryptophan synthase (Chapter 25),184 O-acetylserine sulfhydrylase (cysteine synthase),185 186a and cystathionine (3-synthase (Chapter 24).187 188c In both elimination and (3 replacement an unsaturated Schiff base, usually of aminoacrylate or aminocrotonate, is a probable intermediate (Eq. 14-29). Conversion to the final products is usually assumed to be via hydrolysis to free aminoacrylate, tautomerization to an imino acid, and hydrolysis of the latter, e.g., to pyruvate and ammonium ion (Eq. 14-29). However, the observed stereospecific addition of a... 

Transsulfuration is facilitated by the action of two vitamin Be-dependent enzymes, cystalhionine-p-synthase (CBS), the enzyme deficient in homocystinuria, and cystathionine-Y-lyase (CTH). CBS catalyzes the condensation of homocysteine and serine to cystathionine, and CTH subsequently catalyzes the hydrolysis of cystathionine to cysteine and a-ketobutyrale. Cysteine is important in protein synthesis and taurine synthesis and is a precursor to glutathione, a strong antioxidant and essential compound in detoxification of many xenobiotics [8,10,11]. 

McHale, D., P. Mamalis, and J. Green Partial Racemisation Accompanying the Acid Hydrolysis of Dibenzoyl-D-cystathionine and -lanthionine. J. Chem. Soc. 1960, 2847. 

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