Poisoned Pathways
Fifty years ago,
para
-aminosalicyclic acid (PAS) was developed as an antituberculosis drug. Since then, it has been assumed that PAS acts to competitively inhibit
para
-aminobenzoate (PABA) from entering the folate pathway at the enzyme dihydropteroate synthase (DHPS). Strangely, the well-known inhibitors of DHPS—the sulfonamide drugs—are useless in tuberculosis treatment, although they are effective against other microbial pathogens.
Chakraborty
et al.
(p.
88
, published online 1 November) addressed this conundrum by comparing the effect of several sulfonamides, as well as PAS and PABA, on the folate pathway of live
Mycobacterium tuberculosis.
It seems the bacterium is better at inactivating sulfonamides than PAS and that PAS does not really compete with PABA. Instead, PAS cascades through the folate pathway generating a series of poisonous intermediates.
有毒的途径
五十年前,对于治疗结核病,对氨基水杨酸(PAS)被开发出来作为一种药物。从那时起,人们一直认为PAS通过竞争性抑制对氨基苯甲酸(PABA)进入叶酸途径中的二氢叶酸合酶(DHPS)来发挥作用。奇怪的是,已知的DHPS抑制剂——磺胺类药物——在治疗结核病方面是无效的,尽管它们对其他微生物病原体是有效的。Chakraborty等人(第339卷,第88页,发表于11月1日在线)通过比较几种磺胺类药物、PAS和PABA对结核分枝杆菌的叶酸途径的影响来解决这个难题。看起来,细菌比PAS更擅长失活磺胺类药物,而PAS并不真正与PABA竞争。相反,PAS通过叶酸途径产生一系列有毒中间体。