Zaĭonts V I, Krylov M V, Loskot V I, Kirillov A I
Parazitologiia. 1978 Jan-Feb;12(1):3-8.
The inhibitory analysis has shown that E. tenella does not include ready folic acid into metabolic process but synthesizes its metabolite, 7:8-dihydrofolic acid (DHFA), from its precursor, para-aminobenzoic acid (PABA), which enters the host's organism. PABA can be fully substituted in the process of metabolism by sulphadimesin (SD) at the molar ratio PABA: SD=1: 16.7. As a concurrent antagonist of PABA SD is 6 times stronger in the parasite-host system of Coccidia than in bacteria in cultural medium. The increase in PABA content in relation to SD more than 1: 16.7 intensifies the viability of Coccidia that is expressed in higher lethality of chicks, which reaches its maximum at PABA : SD=1 : 1.25. A further increase in the content of PABA does not affect the host's lethality. The decrease in PABA in relation to SD lower than 1 : 16.7 reduces the viability of Coccidia. Nucleic bases G, A transforming in the organism into corresponding nucleotids and aminoacids, 1-metionin and glycine, which are the products of biosynthesis with a participation of DHFA, do not stimulate the viability of E. tenella that apparently is associated with the non-capability of the host to assimilate timidin.
抑制分析表明，柔嫩艾美耳球虫不将现成的叶酸纳入代谢过程，而是从进入宿主体内的前体对氨基苯甲酸（PABA）合成其代谢产物7,8-二氢叶酸（DHFA）。在代谢过程中，PABA可被磺胺二甲嘧啶（SD）以PABA:SD = 1:16.7的摩尔比完全替代。作为PABA的竞争性拮抗剂，在球虫的寄生虫-宿主系统中，SD的作用比在培养基中的细菌中强6倍。PABA与SD的含量比超过1:16.7时，球虫的活力增强，表现为雏鸡更高的致死率，在PABA:SD = 1:1.25时达到最大值。PABA含量的进一步增加不会影响宿主的致死率。PABA与SD的含量比低于1:16.7时，球虫的活力降低。核酸碱基G、A在体内转化为相应的核苷酸和氨基酸，即1-甲硫氨酸和甘氨酸，它们是在DHFA参与下生物合成的产物，但不会刺激柔嫩艾美耳球虫的活力，这显然与宿主无法同化胸苷有关。
