Table 1.

Role of flavone substituents on the affinity for H₆-NBD2

Flavonoid	Substituents				Apparent Kd, μM*
	3	5	7	4′
Flavone					34.1  ±  11.5
3-hydroxy flavone	OH				10.1  ±  2.5
7-hydroxy flavone			OH		34.9  ±  4.5
Chrysin		OH	OH		8.9  ±  0.3
Galangin	OH	OH	OH		5.3  ±  0.1
Kaempferol	OH	OH	OH	OH	6.7  ±  0.3
Kaempferide	OH	OH	OH	OCH3	4.5  ±  0.2

^*The H₆-NBD2 domain was incubated under conditions of Fig. 2 with increasing concentrations of substituted flavones; the quenching of intrinsic fluorescence was plotted as a function of concentration, and the apparent K_d was determined by using the grafit program. For the different flavones, the average maximal quenching was 100.2 ± 5.9%.