Enzymes are A) tryptophan 2,3-dioxygenase B) kynurenine mono-oxygenase C) kynureninase D) 3-hydroxyanthranilate 3,4,-dioxygenase E) no-enzyme F) Quinolinate phosphoribosyltransferase G) nicotinic acid/nicotinamide mononucleotide adenylyltransferase (Nmnat 1, 2, 3) H) NAD synthetase. I) 2-amino-3-carboxy-muconate-semialdehyde decarboxylase (ACMSD) which acts upon 2-amino-3-carboxy-muconate-semialdehyde to form picolinic acid, as an alternative pathway fed by the kynurenine catabolic pathway, as discussed in the text.