TABLE 2

Derived kinetic constants for LTG glucuronidation by UGT1A3 and UGT1A4 chimeras and mutants Data shown as parameters ± S.E. of parameter fit.


Enzyme

Kma,b or S50c

Vmax d

CLinte or CLmaxf
μM pmol/min/mg μl/min. mg
UGT1A3 N.A. N.A. N.A.
UGT1A3–4 N.A. N.A. N.A.
UGT1A3–4-3 N.A. N.A. N.A.
UGT1A3(I36T) N.A. N.A. N.A.
UGT1A3(H40P) 235 ± 8a 203 ± 1 0.86
UGT1A4 1162 ± 44a 803 ± 9 0.70
UGT1A4–3 341 ± 4a 460 ± 2 1.34
UGT1A4–3-4 1422 ± 21c 2520 ± 26 0.98
UGT1A4(T36I) N.A. N.A. N.A.
UGT1A4(P40H)
1105 ± 10b
63 ± 0.3
0.06
  • N.A., no activity

  • a From fitting to the Michaelis Menten equation

  • b From fitting to the substrate inhibition equation (Ksi = 7695 ± 267 μM)

  • c From fitting to the Hill equation (n = 1.38 ± 0.02)

  • d Normalized for expression relative to UGT1A3

  • e Calculated as Vmax/Km

  • f Calculated according to eq. 4