Table III.

Binding parameters of the spectra induced upon fixation of phenylureas in the active site of CYP76B1

Phenylurea				Ks	ΔAmax × 10−3
	R1	R2	R3
				μm
Monolinuron	−OCH3	−Cl	−H	4.8	6.6
Chlorbromuron	−OCH3	−Br	−Cl	5.3	6.7
Metobromuron	−OCH3	−Br	−H	6.2	7.6
	−CH3	−Cl	−CH3	14.5	5.4
Diuron	−CH3	−Cl	−Cl	20	4.8
Chlortoluron	−CH3	−CH3	−Cl	24	5.1
Isoproturon	−CH3	−CH(CH3)2	−H	55	8.2
	−CH3	−CH3	−CH3	60	6.6
Metoxuron	−CH3	−OCH3	−H	117	6.1

The CYP76B1 concentration was 60 nm in the assays. Difference spectra were recorded after addition of increasing concentrations of ligands to the sample cuvette. An equal volume of the herbicide solvent DMSO was added to the reference. K_s and ΔA_max at saturating ligand concentrations were calculated from the double-reciprocal plots of ΔA_{(390–420nm)} versus substrate concentrations.