Which of the follwoing is a source of norepinephrine?
Norepinephrine is synthesized by a series of enzymatic steps in the adrenal medulla and postganglionic neurons of the sympathetic nervous system from the amino acid tyrosine. Ref: Textbook Of Medical Physiology By Khurana, 2006, Page 769; Lehninger Principles of Biochemistry, 4th Edition, Page 440, 678, 859
Phenylalanine
Alanine
Tyrosine
Tryptophan