Purification and Partial Characterization of Cinnamyl Alcohol Dehydrogenase (CAD) in Striga hermonthica (Del.) Benth

Mannitol is a major compound related to carbon metabolism in the parasitic plant Striga hermonthica despite Mannitol 6-Phosphate Reductase (M6PR) that is the key enzyme of mannitol biosynthesis in plants is likely absent in the parasite. Previous studies suggest that M6PR activity is driven by a Cinnamyl Alcohol Dehydrogenase (CAD) in striga. This work aims to characterize the CAD isoforms of the parasite and to check their activity as M6PR. CAD is purified and characterized from the leaves that display simultaneously high M6PR and CAD activities, using a typical protocol for CAD purification from plants. At least two CAD isoforms, called CADa and CADb, is shown in the leaves, CADa being the major isoform. Only one band characterizes both CADa and CADb in SDS-PAGE, at 38 kDa and 40 kDa respectively. Native isoforms display CAD activity in native gels. CADa has a relatively low affinity for cinnamyl alcohol (Km = 400 µM) and a high stability to heat. Finally, both CADa and CADb do not display M6PR activity and the latter remains unidentified in the protein fraction that does not interact with the 2’ 5’ ADP-Sepharose affinity gel.