TABLE 3

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

Enzyme
Kma or S50b
Hill Coefficient (nH)b
Vmax c
CLintd or CLmaxe
μM pmol/min/mg μl/min/mg
UGT1A3 N.A. N.A. N.A. N.A.
UGT1A3–4 N.A. N.A. N.A. N.A.
UGT1A3–4-3 N.A. N.A. N.A. N.A.
UGT1A3(I36T) N.A. N.A. N.A. N.A.
UGT1A3(H40P) 31 ± 1b 1.34 ± 0.04 121 ± 2 2.21
UGT1A4 40 ± 1a 1119 ± 7 28
UGT1A4–3 58 ± 1b 1.58 ± 0.04 46 ± 1 0.50
UGT1A4–3-4 52 ± 3b 1.62 ± 0.07 72 ± 4 0.71
UGT1A4(T36I) N.A. N.A. N.A. N.A.
UGT1A4(P40H)
28 ± 0.8b
1.28 ± 0.03
83 ± 2
1.75

  • N.A., no activity

  • ↵ a From fitting to the substrate inhibition equation (Ksi = 241 ± 18 μM)

  • ↵ b From fitting to the Hill equation

  • ↵ c Normalized for expression relative to UGT1A3

  • ↵ d Calculated as Vmax/Km

  • ↵ e Calculated according to eq. 4