TABLE 4

Relative catalytic efficiency of eight recombinant human UGTs of the 1A subfamily in glucuronidation of phenolic compounds

Relative catalytic constant (kcat = 1.0) and relative specificity constant (kcat/Km = 1.0) were arbitrarily assigned for the glucuronidation of entacapone by UGT1A9.



1-Hydroxypyrene

4-Nitrophenol

Scopoletin

4-Methylumbelliferone

Entacapone

kcat
Km
kcat/Km
kcat
Km
kcat/Km
kcat
Km
kcat/Km
kcat
Km
kcat/Km
kcat
Km
kcat/Km
μM μM μM μM μM
1A1 0.08 8 0.2 0.09 1039 0.002 0.4 89 0.09 0.03 96 0.01 0.004 42 0.002a
1A1 0.002 17 0.003b
1A3 0.01c 0.02d 0.06 1063 0.002 0.2 500 0.02 0.06 1165 0.003 0.03 259 0.004
1A4 0.002 17 0.001 0.0 0.0 0.0 0.0 0.0 0.0
1A6 0.1 10 0.2 0.6 304 0.2 0.9 194 0.1 0.7 127 0.1 0.0
1A7 0.1 2 4 0.1 240 0.03 0.2 16 0.5 0.3 38 0.3 0.7 23 1.4
1A8 0.1c 0.8d 0.1 2327 0.005 0.2 24 0.6 0.2 330 0.02 0.2 63 0.2
1A9 0.03 0.3 4 0.1 74 0.03 0.1 37 0.1 0.1 16 0.2 1.0 21 1.0
1A10
0.1
0.5
15
0.3
231
0.1
0.6
14
1.6
0.5
30
0.5
0.3
29
0.5
  • a Determined from 3-O-glucuronide.

  • b Determined from 4-O-glucuronide.

  • c kcat calculated from the maximal observed reaction velocity.

  • d kcat/Km determined from the slope of the linear portion of the Michaelis-Menten curve.