Fasciola hepatica: inhibition of phosphoenolpyruvate carboxykinase, and end-product formation by quinolinic acid and 3-mercaptopicolinic acid.

Quinolinic acid and 3-mercaptopicolinic acid act as inhibitors of Fasciola hepatica phosphoenolpyruvate carboxykinase. Low concentrations of these compounds (0.1 mM quinolinate and 0.01 mM 3-mercaptopicolinate) resulted in noncompetitive inhibition, which became mixed inhibition at higher concentrations (1.5 and 0.15 mM, respectively). 3-mercaptopicolinic acid proved to be a much more potent effector than quinolinic acid. Both quinolinic acid and 3-mercaptopicolinic acid caused a significant reduction in the total amount of end product excreted, again 3-mercaptopicolinate being more effective than quinolinate. When glucose was present in the medium, both propionate and acetate levels fell significantly with both inhibitors; however, only 3-mercaptopicolinic acid caused an effect in the absence of glucose.