Table 2.

Substrate specificity of the recombinant F6H Both rF6Hb and rF6Hy were purified on Ni-NTA resin then Superose 12, and fractions were assayed with the indicated substrates, using the direct enzyme assay.

Substratea	Relative enzyme activity (%)
	rF6Hb b	rF6Hy c
3,7,4'-Trimethylquercetin	100	100
3,7-Dimethylquercetin	56	63
3,7,3',4'-Tetramethylquercetin	11	21
3-Methylquercetin	0	4

^a No F6H activity was detected with kaempferol, quercetin, myricetin, naringenin, eriodyctyol, apigenin or luteolin when used as substrate, regardless of concentration. Rhamnetin (7-O-methylquercetin, 17% at 50 μM), tamarixetin (4'-O-methylquercetin, 13 % at 50 μM) and isorhamnetin (3'-O-methylquercetin, 4 % at 50 μM)

^b Estimated as 0.10 pkat/mg for 100% activity and 5 μM substrate.

^c Estimated as 0.19 pkat/mg for 100% activity and 5 μM substrate.