Table 1

Apparent enzyme kinetic parameters for the methylation of catechols catalyzed by recombinant human soluble catecholO-methyltransferase^1-a

Compound	V_max	K_m	V_max/K_m
	nmol/min/mg	μM	ml/min/mg
1 Catechol	48.9 ± 0.9	49.7 ± 1.6	0.98
2 4-Methylcatechol	24.4 ± 0.9	29.1 ± 3.9	0.84
	23.3 ± 1.1	36.7 ± 3.3	0.63
3 4-Isopropylcatechol	36.3 ± 1.7	26.1 ± 3.0	1.39
	6.9 ± 1.5	40.5 ± 27.4	0.17
4 4-tert-Butylcatechol	41.9 ± 2.7	31.9 ± 8.0	1.31
5 4-Chlorocatechol	36.0 ± 0.1	11.7 ± 0.5	3.08
6 3,4-Dihydroxyacetophenone	9.8 ± 0.7	1.4 ± 0.3	7.00
7 3,4-Dihydroxybenz.ac.ethyl ester	7.2 ± 1.7	0.66 ± 0.17	10.9
	3.5 ± 1.1	0.66 ± 0.17	5.30
8 4-Nitrocatechol	0.77 ± 0.09	0.12 ± 0.02	6.42
	0.78 ± 0.05	0.12 ± 0.02	6.50
9 4-tert-Butyl-5-methoxycatechol	32.5 ± 2.4	18.5 ± 2.3	1.76
10 Pyrogallol	53.2 ± 1.5	10.4 ± 0.6	5.12
11 3-Nitrocatechol	0.15 ± 0.02	0.020 ± 0.001	7.50
12 3-Fluorocatechol	30.7 ± 1.8	7.8 ± 1.0	3.94
13 3-Methoxycatechol	39.8 ± 1.8	24.5 ± 2.8	1.62
14 3-Methoxy-5-bromocatechol	17.3 ± 0.9	2.5 ± 0.4	6.92
15 Methylgallate	11.7 ± 0.4	1.0 ± 0.1	11.7
16 Benserazide	41.8 ± 3.6	50.2 ± 7.2	0.83
17 3,5-Dinitrocatechol	N.D.^1-b
18 Tolcapone	N.D.
19 Entacapone	N.D.
20 3,4-Dihydroxybenzoic acid	35.6 ± 0.9	19.9 ± 2.0	1.79
	7.7 ± 0.1	28.3 ± 0.4	0.27
21 2,3-Dihydroxybenzoic acid	N.D.
22 3,4-Dihydroxyphenyl acetic acid	34.0 ± 2.2	68.8 ± 10.8	0.49
	4.0 ± 0.1	53.7 ± 4.0	0.074
23 3,4-Dihydroxymandelic acid	43.7 ± 2.0	132 ± 11	0.33
24 3,4-Dihydroxyphenylglycol	37.2 ± 1.4	46.4 ± 4.7	0.80
25 Caffeic acid	25.9 ± 1.9	3.2 ± 0.7	8.09
	15.5 ± 0.2	2.8 ± 0.1	5.54
26 Hydrocaffeic acid	31.5 ± 1.7	25.4 ± 4.5	1.24
	12.1 ± 0.03	45.1 ± 0.3	0.27
27 Dopamine	35.9 ± 1.4	188 ± 16	0.19
28 5-Hydroxydopamine	46.7 ± 1.1	61.6 ± 4.1	0.76
29 6-Hydroxydopamine	25.3 ± 2.0	244 ± 32	0.10
30 l-Noradrenaline	33.2 ± 0.8	256 ± 20	0.13
31 l-Adrenaline	44.0 ± 1.0	132 ± 13	0.33
32 Isoprenaline	25.8 ± 0.6	145 ± 8.5	0.18
	3.1 ± 0.3	170 ± 31	0.018
33 Dobutamine	29.0 ± 0.9	23.7 ± 3.1	1.22
	6.9 ± 0.5	28.6 ± 7.5	0.24
34 l-DOPA	29.8 ± 0.9	564 ± 28	0.053
35 α-Methyl-DOPA	21.4 ± 0.7	1789 ± 108	0.012
	2.6 ± 0.3	1170 ± 309	0.002
36 S(−)-Carbidopa	14.3 ± 0.8	599 ± 63	0.024
37 l-DOPA methyl ester	44.2 ± 0.7	51.1 ± 2.9	0.86
38 Tetrachlorocatechol	0.62 ± 0.03	0.029 ± 0.002	21.4
39 2,3-Dihydroxynaphthalene	30.8 ± 1.6	1.5 ± 0.3	20.5
40 6,7-Dihydroxycoumarin	3.3 ± 0.03	0.30 ± 0.01	11.0
41 1-Methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline	18.3 ± 0.9	29.4 ± 3.7	0.62
	10.6 ± 0.1	36.2 ± 0.2	0.29
42 SKF 38393	5.0 ± 0.04	67.2 ± 1.2	0.074
	10.5 ± 0.5	73.6 ± 8.3	0.14
43 2-Hydroxyestradiol	32.4 ± 2.6	3.7 ± 1.1	8.76
	13.7 ± 1.8	4.2 ± 2.2	3.26
44 4-Hydroxyestradiol	31.5 ± 2.5	12.4 ± 2.6	2.54
45 Dihydrexidine	10.1 ± 2.3	25.0 ± 14.5	0.40
	10.5 ± 6.2	53.1 ± 50.6	0.20
46 Apomorphine	N.D.

↵1-a The enzyme kinetic parameters were determined as described under Materials and Methods.
↵1-b N.D., no methylation detected; the highest substrate concentration tested was 500 μM.