Model/Equation | V_{max} | K_{s} | K_{a} | K_{i} | α | β | |
---|---|---|---|---|---|---|---|
pmol/min/pmol CYP | μM | ||||||
3HDZ formation and activation by TS | Model 1C/eq.5 ^{2-a} | 21 (1.2) | 638 (41) | 148 (40) | 0.1 (0.02) | 2^{2-b} | |
Model 1B/eq. 4 | 24 (2) | 694 (112) | 137 (55) | 0.1 (0.04) | 2.0 (0.2) | ||
NDZ formation and activation by TS | Model 1B/eq. 4 | 3.9 (0.1) | 407 (41) | 38 (3) | 0.2 (0.04) | 1.8 (0.1) | |
6β-HTS formation and inhibition by DZ | Model 1D/eq. 6 | 19 (0.2) | 137 (12) | 186 (6) | 0.1 (0.02) | 2^{2-b} |
The kinetic parameters were determined using rate equation models as listed above using GRAFIT v3.0 (Erithacus Software Ltd). Values in parentheses represent standard error values.
↵2-a The data set at the highest testosterone concentration is excluded from the fit to model 1C because there is a combination of activation and inhibition occurring at the high concentrations suggesting a competitive process, as described by model 1B.
↵2-b Assuming that the catalytic sites are equivalent, β is equal to 2 in the equation and cancels out because V_{max} is equal to 2K_{p}/[E]_{t}, where [E]_{t} is the total enzyme concentration.