FPGS activity and polyglutamylation formations in wild-type and MTX- and 7-OHMTX-resistant cells. (A,C) FPGS activity in parental CCRF-CEM (A) and MOLT-4 (C) cells and their MTX- or 7-OHMTX-resistant sublines. Enzyme activity ± SD is depicted relative to parental cells (100%). Control values for FPGS activity in parental CCRF-CEM cells and MOLT-4 cells were 958 ± 478 and 739 ± 171 pmol [³H]-glutamate incorporated/mg protein/hour, respectively. (B,D) [³H]MTX-polyglutamate formation in parental CCRF-CEM (B) and MOLT-4 (D) cells and their MTX- and 7-OHMTX sublines after 24 hours of exposure to 1 μM[³H]-MTX. Formation of individual polyglutamate conjugates is depicted as percentage of total [³H]MTX accumulation. Total [³H]MTX accumulation (expressed as pmol [³H]-MTX/10⁷ cells) after 24 hours for the individual cell lines were as follows: CCRF-CEM, 63.3 ± 1.8; CCRF-CEM/MTX, 26.5 ± 2.4; CCRF-CEM/7-OHMTX, 32.9 ± 1.3; MOLT-4, 70.5 ± 1.2; MOLT-4/MTX, 18.2 ± 4.1; and MOLT-4/7-OHMTX, 22.1 ± 0.7 pmol/10⁷ cells. Results are presented as means ± SD of 3 separate experiments.