Evolutionary History of Lignins - Botanical Research - page 335

and coniferyl alcohol ( Ros Barcel ´ et al., 2004 ). However, this situation is
not so clear in the case of sinapyl alcohol; in this case, typical acidic perox-
idases, with some exceptions ( Christensen et al., 1998 ), are generally regarded
as poor catalysts.
Theoretical comparative models between Zinnia elegans S peroxidase and
Arabidopsis thaliana G peroxidase showed two important differences
( Fig. 10 ). Helix D 0 in Arabidopsis fixes the motif which determines the
conformation and hydrophobicity of the substrate-binding site ( Østergaard
et al., 2000 ) and it is absent in S peroxidases ( Ros Barcel ´ et al., 2007 ). On the
contrary, there is a novel b -strand in S peroxidases that influences the
catalytic centre of the enzymes. All of these factors are likely to condition
the substrate specificity of S peroxidases, determining the unique catalytic
properties ( G ´ mez Ros et al., 2007a; Ros Barcel ´ et al., 2007 ).
G ´ mez Ros et al. (2007a) determined the structural motifs of S peroxi-
dases, by alignment of the amino acid sequence of a set of peroxidases whose
capacity for oxidizing S moieties is well known ( Gabald ´ n et al., 2005;
Quiroga et al., 2000; Sasaki et al., 2006; Takeda et al., 2003 ) with two typical
G peroxidases ( Nielsen et al., 2001; Østergaard et al., 2000 ).
Searching through protein databases for other S peroxidases in angios-
perms showed that the determinants of S peroxidases have been conserved
Fig. 10. Predicted 3D structure of the Arabidopsis thaliana ATP A2 G peroxidase
(A) and the Zinnia elegans S peroxidase (B). Adapted from Ros Barcel ´ et al. (2007) ,
reproduced with permission from Elsevier.