{PDOC00424}
{PS00488; PAL_HISTIDASE}
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* Phenylalanine and histidine ammonia-lyases active site *
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Phenylalanine ammonia-lyase (EC 4.3.1.5) (PAL) is  a  key  enzyme of plant and
fungi  phenylpropanoid  metabolism  which is involved in the biosynthesis of a
wide  variety  of secondary metabolites such  as  flavanoids,   furanocoumarin
phytoalexins and  cell  wall  components.  These compounds have many important
roles in plants during normal growth and in responses to environmental stress.
PAL catalyzes  the  removal  of  an  ammonia  group from phenylalanine to form
trans-cinnamate.

Histidine ammonia-lyase (EC 4.3.1.3) (histidase)  catalyzes  the first step in
histidine degradation, the removal of  an  ammonia  group  from  histidine  to
produce urocanic acid.

The two types of enzymes are functionally and  structurally related [1].  They
are the only enzymes  which are known to have the modified amino acid dehydro-
alanine (DHA) in their active site. A serine residue has been shown [2,3,4] to
be the  precursor  of  this  essential electrophilic moiety. The region around
this active  site  residue  is  well  conserved and can be used as a signature
pattern.

-Consensus pattern: [GS]-[STG]-[LIVM]-[STG]-[SAC]-S-G-[DH]-L-x-[PN]-L-[SA]-
                    x(2,3)-[SAGVTL]
                    [S is the active site residue]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: April 2006 / Pattern revised.

[ 1] Taylor R.G., Lambert M.A., Sexsmith E., Sadler S.J., Ray P.N.,
     Mahuran D.J., McInnes R.R.
     "Cloning and expression of rat histidase. Homology to two bacterial
     histidases and four phenylalanine ammonia-lyases."
     J. Biol. Chem. 265:18192-18199(1990).
     PubMed=2120224
[ 2] Langer M., Reck G., Reed J., Retey J.
     "Identification of serine-143 as the most likely precursor of
     dehydroalanine in the active site of histidine ammonia-lyase. A study
     of the overexpressed enzyme by site-directed mutagenesis."
     Biochemistry 33:6462-6467(1994).
     PubMed=8204579
[ 3] Schuster B., Retey J.
     "Serine-202 is the putative precursor of the active site
     dehydroalanine of phenylalanine ammonia lyase. Site-directed
     mutagenesis studies on the enzyme from parsley (Petroselinum crispum
     L.)."
     FEBS Lett. 349:252-254(1994).
     PubMed=8050576
[ 4] Taylor R.G., McInnes R.R.
     "Site-directed mutagenesis of conserved serines in rat histidase.
     Identification of serine 254 as an essential active site residue."
     J. Biol. Chem. 269:27473-27477(1994).
     PubMed=7961661

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