TABLE 2.

Inhibition constants (K_i) of enzymes involved in nucleotide biosynthesis for MTX and its polyglutamates (Allegra et al., 1985a,b; Drake et al., 1987; Baram et al., 1988; Sant et al., 1992)

Ki	MTX-PG1	MTX-PG2	MTX-PG3	MTX-PG4	MTX-PG5
	µM
DHFR	11.0 × 10−5	17.0 × 10−5	8.0 × 10−5		8.0 × 10−5
TS	13.0	0.17	0.14	0.13	0.047
AICART	143.9	5.47	0.56	0.056	0.057
GART	80	57	7.1	5.1	2.5
ATase	ND				550

ND, no inhibition was detected.