PROSITE documentation PDOC00677
Cys/Met metabolism enzymes pyridoxal-phosphate attachment site


A number of pyridoxal-dependent enzymes involved in the metabolism of cysteine, homocysteine and methionine have been shown [1,2] to be evolutionary related. These are:

  • Cystathionine γ-lyase (EC (γ-cystathionase), which catalyzes the transformation of cystathionine into cysteine, oxobutanoate and ammonia. This is the final reaction in the transulfuration pathway that leads from methionine to cysteine in eukaryotes.
  • Cystathionine γ-synthase (EC, which catalyzes the conversion of cysteine and succinyl-homoserine into cystathionine and succinate: the first step in the biosynthesis of methionine from cysteine in bacteria (gene metB).
  • Cystathionine β-lyase (EC (β-cystathionase), which catalyzes the conversion of cystathionine into homocysteine, pyruvate and ammonia: the second step in the biosynthesis of methionine from cysteine in bacteria (gene metC).
  • Methionine γ-lyase (EC (L-methioninase) which catalyzes the transformation of methionine into methanethiol, oxobutanoate and ammonia.
  • OAH/OAS sulfhydrylase, which catalyzes the conversion of acetylhomoserine into homocysteine and that of acetylserine into cysteine (gene MET17 or MET25 in yeast).
  • O-succinylhomoserine sulfhydrylase (EC 4.2.99.-).
  • Yeast hypothetical protein YGL184c.
  • Yeast hypothetical protein YHR112c.

These enzymes are proteins of about 400 amino-acid residues. The pyridoxal-P group is attached to a lysine residue located in the central section of these enzymes; the sequence around this residue is highly conserved and can be used as a signature pattern to detect this class of enzymes.

Last update:

December 2004 / Pattern and text revised.


Technical section

PROSITE method (with tools and information) covered by this documentation:

CYS_MET_METAB_PP, PS00868; Cys/Met metabolism enzymes pyridoxal-phosphate attachment site  (PATTERN)


1AuthorsOno B.I. Tanaka K. Naito K. Heike C. Shinoda S. Yamamoto S. Ohmori S. Oshima T. Toh-E A.
TitleCloning and characterization of the CYS3 (CYI1) gene of Saccharomyces cerevisiae.
SourceJ. Bacteriol. 174:3339-3347(1992).
PubMed ID1577698

2AuthorsBarton A.B. Kaback D.B. Clark M.W. Keng T. Ouellette B.F.F. Storms R.K. Zeng B. Zhong W.W. Fortin N. Delaney S. Bussey H.
TitlePhysical localization of yeast CYS3, a gene whose product resembles the rat gamma-cystathionase and Escherichia coli cystathionine gamma-synthase enzymes.
SourceYeast 9:363-369(1993).
PubMed ID8511966

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