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 4.4.1.1) (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 2.5.1.48), 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 4.4.1.8) (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 4.4.1.11) (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.
Barton 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.
Title
Physical localization of yeast CYS3, a gene whose product resembles the rat gamma-cystathionase and Escherichia coli cystathionine gamma-synthase enzymes.
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