Synthesis of MLT. MLT synthesis takes place in pineal gland. Pineal glands uptake tryptophan and converts it into MLT through five enzymes catalyzed reactions. The diagram represents the sequential reactions and enzymes involved in biosynthesis of MLT. TPH: Tryptophan hydroxylase, 5-HTPD: 5-Hydroxytryptophan decarboxylase, SNAT: Serotonin N-acetyltransferase, HIOMT: hydroxyindole-O-methyl transferase).