Table 3

Apparent enzyme kinetic parameters for the methylation of catechols catalyzed by recombinant rat soluble catecholO-methyltransferase3-a

CompoundVmaxKmVmax/Km
nmol/min/mg μM ml/min/mg
 1 Catechol184  ± 10250  ± 220.74
 2 4-Methylcatechol82.8  ± 5.7124  ± 170.67
97.6  ± 6.4156  ± 200.63
 3 4-Isopropylcatechol155  ± 775.3  ± 11.82.06
50.0  ± 4.9104  ± 280.48
 4 4-tert-Butylcatechol156  ± 699.9  ± 7.51.56
 5 4-Chlorocatechol138  ± 420.3  ± 1.16.80
 7 3,4-Dihydroxybenz.ac.ethyl ester28.4  ± 1.42.3  ± 0.512.3
15.9  ± 0.32.4  ± 0.26.63
 8 4-Nitrocatechol3.2  ± 0.1<5.0>0.64
5.9  ± 0.9<5.0>1.18
16 Benserazide134  ± 3105  ± 61.28
17 3,5-Dinitrocatechol N.D.3-b
18 TolcaponeN.D.
19 EntacaponeN.D.
20 3,4-Dihydroxybenzoic acid110  ± 0.197.0  ± 0.51.13
23.8  ± 0.871.7  ± 9.20.33
21 2,3-Dihydroxybenzoic acidN.D.
22 3,4-Dihydroxyphenyl acetic acid90.6  ± 3.0275  ± 190.33
8.3  ± 2.0180  ± 1320.046
27 Dopamine133  ± 1826  ± 280.16
34 l-DOPA104  ± 71870  ± 1930.056
36 S(−)-Carbidopa53.1  ± 2.51988  ± 1290.027
39 2,3-Dihydroxynaphthalene121  ± 113.2  ± 0.737.8
43 2-Hydroxyestradiol95.8  ± 0.814.3  ± 0.46.70
61.4  ± 9.915.0  ± 7.74.09
44 4-Hydroxyestradiol86.9  ± 2.227.5  ± 2.33.16
45 Dihydrexidine50.1  ± 3.129.9  ± 7.51.68
23.6  ± 2.932.0  ± 13.30.74
46 ApomorphineN.D.

  • ↵3-a  The enzyme kinetic parameters were determined as described under Materials and Methods.

  • ↵3-b  N.D., no methylation detected, the highest substrate concentration tested was 500 μM.