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* Fatty acid desaturases signatures *
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Fatty acid desaturases (EC 1.14.99.-)  are enzymes that catalyze the insertion
of a double bond at the delta position of fatty acids.

There seems to be two distinct families of fatty acid desaturases which do not
seem to be evolutionary related.

Family 1 is composed of:

 - Stearoyl-CoA desaturase (SCD) (EC 1.14.99.5) [1].  SCD is  a key regulatory
   enzyme of unsaturated fatty acid biosynthesis. SCD introduces a cis  double
   bond at the delta(9) position of fatty acyl-CoA's such as palmitoleoyl- and
   oleoyl-CoA. SCD is a membrane-bound enzyme that is thought to function as a
   part of a multienzyme  complex in the  endoplasmic reticulum of vertebrates
   and fungi.

As a signature pattern  for this family  we selected a conserved region in the
C-terminal part of these enzymes,  this region  is rich  in histidine residues
and in aromatic residues.

Family 2 is composed of:

 - Plants stearoyl-acyl-carrier-protein desaturase  (EC 1.14.99.6) [2],  these
   enzymes catalyze the introduction of a double bond at the delta(9) position
   of steraoyl-ACP to produce oleoyl-ACP.  This enzyme  is responsible for the
   conversion of saturated  fatty  acids  to  unsaturated  fatty  acids in the
   synthesis of vegetable oils.
 - Cyanobacteria desA [3]  an  enzyme  that  can introduce a second cis double
   bond  at  the  delta(12)   position  of  fatty   acid  bound  to  membranes
   glycerolipids. DesA is involved in chilling tolerance; the phase transition
   temperature of lipids of cellular membranes being dependent on  the  degree
   of unsaturation of fatty acids of the membrane lipids.

As a signature pattern  for this family  we selected a conserved region in the
C-terminal part of these enzymes.

-Consensus pattern: G-E-x-[FY]-H-N-[FY]-H-H-x-F-P-x-D-Y
-Sequences known to belong to this class detected by the pattern: ALL family 1
 enzymes.
-Other sequence(s) detected in SWISS-PROT: NONE.

-Consensus pattern: [ST]-[SA]-x(3)-[QR]-[LI]-x(5,6)-D-Y-x(2)-[LIVMFYW]-[LIVM]-
                    [DE]-x-L
-Sequences known to belong to this class detected by the pattern: ALL family 2
 enzymes.
-Other sequence(s) detected in SWISS-PROT: NONE.

-Expert(s) to contact by email: Piffanelli P.
                                piffanelli@jii.afrc.ac.uk

-Last update: October 1993 / Patterns and text revised.

[ 1] Kaestner K.H., Ntambi J.M., Kelly T.J. Jr., Lane M.D.
     J. Biol. Chem. 264:14755-14761(1989).
[ 2] Shanklin J., Somerville C.R.
     Proc. Natl. Acad. Sci. U.S.A. 88:2510-2514(1991).
[ 3] Wada H., Gombos Z., Murata N.
     Nature 347:200-203(1990).