. 1998 Sep;42(9):2221–2224. doi: 10.1128/aac.42.9.2221

TABLE 1.

Biochemical properties of DHFR types I, Ib, V, VI, VII, and XV^a

DHFR	Tmp ID₅₀ (μM)	Mtx ID₅₀ (μM)	FH₂K_m (μM)	Tmp K_i (μM)	TD₅₀ min
I	57.0	4.4	5.6	7.4	0.5
Ib	32.0	2.8	11.0	41	1.2
V	23.0	3.5	15.5	3.2	—^b
VI	200.0	7.3	31.2	75.0	0.4
VII	30.0	3.0	20.0	7.0	1.5
XV	22.4	4.4	16.7	15.9	>20

Data for DHFR types I (20), Ib (30), V (27), VI (28), and VII (7) come from previous reports. Tmp, trimethoprim; Mtx, methotrexate; TD₅₀, time required to inhibit DHFR activity by 50% at 45°C.

—, Dependent on protein concentration.