Parasitic apicomplexans harbor a chlorophyll a-D1 complex, the potential target for therapeutic triazines.

Ultrastructural evidence is presented for the presence of plastid-like organelles in Toxoplasma gondii, Sarcocystis muris, Babesia ovis, and Plasmodium falciparum. In addition, it was shown that merozoites of T. gondii contain protochlorophyllidae a and traces of chlorophyll a bound to the photosynthetic reaction centers I PS I and PS II. A psbA gene was isolated from merozoites of S. muris by the polymerase chain reaction (PCR). Partial sequencing of the PCR product revealed that the herbicide-binding region is highly conserved. Therefore, it is likely that the sensitivity of apicomplexans to the herbicide toltrazuril depends on the interaction of the herbicide with the D1 protein of the photosynthetic reaction center of the parasite's organelles.