Dopamine Biosynthesis Neurotransmitters Module: The Beery Twins’ Story© A Project-Based Learning Activity Sepiapterin reductase is the final enzyme in the biosynthetic pathway for tetrahydrobiopterin – a cofactor used by other enzymes in the synthesis of the neurotransmitters dopamine and serotonin. In the case of dopamine biosynthesis, the enzyme tyrosine hydroxylase uses tetrahydrobiopterin to convert tyrosine to L-DOPA. In a second reaction, the enzyme aromatic L-amino acid decarboxylase converts L-DOPA into dopamine, the active neurotransmitter. Enzymes Neurotransmitters Cofactors Tetrahydrobiopterin Pathway Dopamine Pathway Guanosine Triphosphate (GTP) Tyrosine GTP Cyclohydrolase I (GCH1) Tyrosine Hydroxylase (TH) with Tetrahydrobiopterin Cofactor Pyruvoyl-Tetrahydropterin Synthase (PTPS) 6-Pyruvoyl-Tetrahydropterin L-DOPA Aromatic L-Amino Acid Decarboxylase (AAAD) Sepiapterin Reductase (SPR) with Vitamin B6 Cofactor Tetrahydrobiopterin Dopamine Version 1.4 -12/2015 ...where molecules become real TM http://cbm.msoe.edu www.3dmoleculardesigns.com Dopamine Biosynthesis Model Guide Neurotransmitters Module: The Beery Twins’ Story© A Project-Based Learning Activity TH AAAD Tyrosine L-DOPA Dopamine Tyrosine (Tyr or Y) is a non-essential amino acid L-DOPA (L-3,4-dihydroxyphenylalanine), an The nal step in the dopamine biosynthesis that can be synthesized in the human body from intermediate molecule in the dopamine biosynthesis pathway requires the removal of the the amino acid phenylalanine. Tyrosine is pathway, is formed by the addition of a hydroxyl carboxylic acid group (COOH) from the composed of the standard amino acid backbone group to the third carbon of the aromatic ring of backbone of the L-DOPA to form the with an aromatic ring containing a hydroxyl (OH) tyrosine. L-DOPA can cross the blood-brain barrier. neurotransmitter dopamine. group on the fourth carbon of the ring. Dopamine cannot. Version 1.4 -12/2015 Neurotransmitter (Dopamine) Model Color Key TH Tyrosine Hydroxylase Oxygen Carbon (requires tetrahydrobiopterin as a cofactor) Hydrogen* Nitrogen ...where molecules become real TM AAAD Aromatic L-Amino Acid Decarboxylase http://cbm.msoe.edu (requires vitamin B6 as a cofactor) * Hydrogens not shown in chemical drawings www.3dmoleculardesigns.com.