Fig. 3.

Ketotifen increases the activity of hDHFR. A) Schematic outline of the conversion of 7,8-dihydrofolate (DHF) to 5,6,7,8-tetrahydrofolate (THF) through the enzymatic action of human dihydrofolate-reductase (hDHFR). The reaction involves the oxidation of NADPH_2, which can be measured at OD₃₄₀. B) Ketotifen (KETO) caused a significant concentration-dependent increase in the conversion of DHF to THF (as measured by oxidation of NADPH₂ over 10 min) by recombinant hDHFR. The NADPH₂ oxidation is indicative of hDHFR activity. The bars indicate mean values at equilibrium of biological triplicates and are shown ± standard deviation. *** (p < 0.001) and ** (p < 0.01) indicate a statistically significant difference in hDHFR activity in the presence of ketotifen, relative to the activity measured in the absence of ketotifen (Student's unpaired t-test). Time courses for the conversion of DHF to THF are shown in Supplementary Fig. S3.