Fig 6. Proposed model illustrating transport dynamics and pyrimidine salvage activities that mediate the metabolic conversion of fluoropyrimidines in A. fumigatus.

The major route of 5FC metabolic activation is catalyzed by FcyA and Uprt (black arrows). UdpB, UrhB and UrkA constitute enzymes of a metabolic bypass (grey arrows) that generates 5FUMP, however in a less efficient way. During 5FC treatment, intracellular levels of 5FC, 5FU, 5FUR and so far unknown fluoropyrimidine antimetabolites are reduced by their export into the environment.