Oxygenase activity was measured with 10μg of protein construct and 200μM LA as the substrate using an oxygen electrode as described under “Experimental Procedures”. A value of 100% is assigned for the oxygenase activity of wild-type Ath α-DOX, with mutant activity normalized to the wild-type construct. Values represent the average of 3 trials. Values for Osa α-DOX are from (9). The residue numbering equivalences between Ath and Osa α-DOX are as follows: Q159:Q153; H318:H311; T323:T316; Y386:Y379; R565:R558; R566:R559. ND, not determined.