Brequinar and orotate inhibit whereas uridine has no effect on in vitro DHODH enzymatic activity. (A) Representative enzymatic kinetics of purified recombinant DHODH in the presence and absence of brequinar, orotate, and uridine. (B) Quantitative analysis of DHODH enzymatic activity in the presence and absence of brequinar, orotate, and uridine. Error bars are standard deviations of triplicate experiments. *P < 0.05, **P < 0.01, ***P < 0.001 versus DHODH control. P values were calculated using Excel's paired Student t-test function.