Early work on the biochemistry of coccidia has been reviewed by Wang (1982). None of the coccidia, including T. gondii, have been grown in cell-free medium. Toxoplasma gondii is incapable of purine synthesis and depends entirely on the host cell for preformed purines (Pfefferkorn 1990). Several purine and pyrimidine salvage enzymes have been identified (Pfefferkorn 1990; Iltzsch 1993; Manafi et al. 1993). Toxoplasma gondii appears only to be able to salvage uracil, and although it can convert thymine to thymidine, there is no salvage pathway for thymidine (Iltzsch 1993; Pfefferkorn and Pfefferkorn 1977).
Toxoplasma gondii cannot use preformed folates as mammalian cells can; the dihydrofolate reductase (DHFR) enzyme is therefore a major target for antibiotic agents against T. gondii (Derouin and Chastang 1989; Roos 1993). Little is known about the lipids and carbohydrates of T. gondii. The parasite has a low cholesterol/phospholipid ratio, many unsaturated fatty acid chains, and large amounts of phosphatidylcholine (Gallois et al. 1988). A 6-kDa carbohydrate antigen seems to be responsible for early T. gondii-specific IgM antibody production, and it appears that T. gondii is capable of both N- and O-glycosylation (Schwartz and Tomavo 1993).
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