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* Cys/Met metabolism enzymes pyridoxal-phosphate attachment site *
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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   gamma-lyase   (EC 4.4.1.1)   (gamma-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  gamma-synthase (EC 4.2.99.9), 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 beta-lyase (EC 4.4.1.8) (beta-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).
 - OAH/OAS sulfhydrylase, which  catalyzes  the conversion of acetylhomoserine
   into homocysteine  and  that  of  acetylserine into cysteine (gene MET17 or
   MET25 in yeast).

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.

-Consensus pattern: D-[LIVM]-x(3)-[SAGC](2)-T-K-[YW]-[LIVM]-x-G-H-[SG]
                    [K is the pyridoxal-P attachment site]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in SWISS-PROT: NONE.
-Last update: October 1993 / First entry.

[ 1] Ono B.I., Tanaka K., Naito K., Heike C., Shinoda S., Yamamoto S.,
     Ohmori S., Oshima T., Toh-E A.
     J. Bacteriol. 174:3339-3347(1992).
[ 2] 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.
     Yeast 9:363-369(1993).