Table 3.
Deiodinase isozyme specificity of cell line lysates as measured by LC-MS/MS using selected iodothyronines as substrates
| HepG2 | MSTO-211H | ECC-1 | HEK293 | |
|---|---|---|---|---|
| Dio1 | ||||
| Km(μm rT3) | 0.59 ± 0.03 | ND | see text | ND |
| Vmax(pmol 3,3′-T2/mg protein·min) | 2.2 ± 0.06 | |||
| Dio2 | ||||
| Km(μm rT3) | ND | 0.005 ± 0.001 | ND | ND |
| Vmax(pmol 3,3′-T2/mg protein·min) | 0.130 ± 0.026 | |||
| Dio3 | ||||
| Km(μm T3) | ND | ND | 0.006 ± 0.002 | ND |
| Vmax(pmol 3,3′-T2/mg protein·min) | 2.9 ± 0.2 |
The apparent Km and Vmax values were determined by LC-MS/MS-based deiodinase assays using an incubation time of 30 min and the following substrates: 50 nm to 4.4 μm rT3 for Dio1, 10–50 nm rT3 for Dio2, and 10–100 nm T3 for Dio1. The values represent the mean ± sd from three separate experiments performed in triplicate. ND, Not detected.