Table III.

Substrate specificity of Serratula flavonol 3-O-methyltransferase^ab

Substrate	Relative Activity	Km value	Vmax	Vmax/Km
	%c	μm	pkat mg−1
Q	100	12	61	5.08
Kaempferol	93	13	169	13
Myricetin	46	7	15	2.14

The enzyme protein fraction II eluted from the Mono-Q column (Fig. 3A) was assayed against the indicated substrates at a concentration of 50 μm as described in “Materials and Methods”.

^aSee Figure 1 for structures of the substrates used.

^bNo OMT activity was detected with either catechol, caffeic acid, caffeoyl CoA, or 3-MeQ, nor with naringenin, eriodyctiol, apigenin, or luteolin when used as substrates. Other substrates were accepted to varying degrees (% of control); these are: isorhamnetin (88%), tamarixetin (85%), herbacetin (33%), rhamnetin (13%), galangin (60%), quercetagetin (39%), and gossypetin (38%).

^cEquivalent to a specific activity of 3.26 pkat g⁻¹.