Microsomal canine P450 probe substrates, kinetics, isoform selectivity, and transitions used to quantify metabolites
P450 Isoform Implicated | Substratea | Metabolite | V b | Km b | Reported Selectivityc | Q1→Q3d |
|---|---|---|---|---|---|---|
| nmol/min/nmol total P450 | μM | |||||
| 1A1/1A2 | Phenacetin | 4-Acetamidophenol | 0.79 ± 0.25 | 54 ± 30 | 6 | 152→110 |
| 2B11 | Temazepam | Oxazepam | 6.4 ± 0.2 | 82 ± 7 | ∼10 | 287→241 |
| 2C21/2C41 | Diclofenac | 4′-OH | 0.99 ± 0.03 | 29 ± 8 | 5 | 312→231 |
| 2D15 | Bufuralol | 1′-OH | 4.0 ± 0.1 | 5.7 ± 0.7 | 8 | 278→186 |
| 3A12/26 | Midazolam | 1′-OH | 0.27 ± 0.05 | 1.5 ± 0.5 | N.D. | 342→203 |
|
| Triazolam (internal standard) |
|
|
|
| 343→308 |
N.D., not determined
↵ a Except for midazolam, substrates were chosen for their selective turnover to specific metabolites as assessed by a panel of recombinant canine P450s (Shou et al., 2003; Lu et al., 2005)
↵ b ± represents the error of the parameter estimate derived from nonlinear regression
↵ c Rate of metabolite formed per mole of recombinant P450 versus the amount formed by the isoform producing the second highest amount of metabolite
↵ d Transition monitored in triple quadrupole mass spectrometer using positive ionization