Tryptophan is glucogenic & ketogenic by producing

The major metabolic fate of tryptophan is to be oxidized by tryptophan pyrrolase (tryptophan di-oxygenase) (Step 1, Fig. 17.8). It is a hemoprotein. The enzyme is inducible by coicosteroids.iii. In this major pathway, the total 11 carbon atoms of tryptophan are catabolized as formyl group (1C which enters the one-carbon pool), alanine (3C, entering the glucose pathway) and acetoacetate (4C, going to ketogenic pathway). So, tryptophan is both glucogenic and ketogenic. The remaining 3 carbons are removed as 3 CO2 molecules.Ref: DM Vasudevan - Textbook of Biochemistry, 6th edition, page no: 211