Table 2

Apparent K m values for thyroid hormone sulfation by hST1B2, hP-PST-1, and hM-PST

Expressed STThyroid hormone apparentKm
ST1B223  ± 9NC2-a 141  ± 2851  ± 14
P-PST-1Trace2-b 15  ± 8Trace2-b 2.3  ± 0.5
M-PSTTrace2-b 20  ± 3Trace2-b 26  ± 4

Each value represents the average ± standard deviation of three separate determinations of the apparent K m using the EnzymeKinetics programs. The human ST activities were expressed inE. coli XL1-Blue cells using the pKK233-2 vector as described in the text.

    • 2-a An apparent K m value could not be calculated from the ascending portion of the concentration curve (0.5–10 μm) using the EnzymeKinetics programs.

    • 2-b The levels of activity were too low to be reliably measured (<0.025 pmol sulfated/min).