Table 2

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

Expressed ST	Thyroid hormone apparentK_m
Expressed ST	T4	T3	rT3	3,3′-T2
	m
ST1B2	23 ± 9	NC^2-a	141 ± 28	51 ± 14
P-PST-1	Trace^2-b	15 ± 8	Trace^2-b	2.3 ± 0.5
M-PST	Trace^2-b	20 ± 3	Trace^2-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).