FIGURE 6.

Consolidated binding pocket model for cis- and trans-desaturases and acetylenases. To accommodate the regiospecific production of (12E)-alkenes in all of the methyl-proximal acetylenases, the alkyl chain at C12-C13 is preorganized within a 90–120° dihedral angle window. Within these bounds, the projection of C13 normal to the linoleate-defined plane for a cis-desaturation is minimized, whereas the vinyl C-H bond orientation is constrained. Torsion about the C12-C13 bond coordinated with H13 abstraction is postulated to lead to cis- and trans-alkenes.