In vitro assay for ABA 8'-hydroxylase: implications for improved assays for cytochrome P450 enzymes.

In vitro assays for cytochrome P450 enzymes developed from plant-derived microsomal extracts have not been used extensively for the characterization and quantification of enzyme activities in plant tissues. We describe here an in vitro assay for abscisic acid (ABA) 8'-hydroxylase that was developed using microsomes extracted from (+)-ABA-induced corn suspension cultures. This assay may be useful for further characterization and monitoring of ABA 8'-hydroxylase activities in germinating seeds, seedlings, and other tissues. Additionally, the optimization protocols provided here may be adapted towards improving in vitro enzyme assays for other cytochrome P450 enzymes expressed in plants.