A Minimal Kynurenine Pathway Was Preserved for Rhodoquinone but Not for NAD Biosynthesis in Parasitic Worms: The Essential Role of NAD Rescue Pathways.

To determine the role of the kynurenine (KYN) pathway in rhodoquinone (RQ) and NAD biosynthesis and whether NAD rescue pathways are essential in parasitic worms (helminths). We demonstrate that RQ, the key electron transporter used by helminths under hypoxia, derives from the tryptophan (Trp) catabolism even in the presence of a minimal KYN pathway. We show that of the KYN pathway genes only the kynureninase and tryptophan/indoleamine dioxygenases are essential for RQ biosynthesis.