Its vasodilating effect increases blood flow to the sexual organs, making orgasm more intense, and it has been used to treat rheumatoid arthritis.  
An electron donor, it neutralizes singlet oxygen and the hydroxyl radical in the heart.   Its vasodilating effect increases blood flow to the sexual organs, making orgasm more intense, and it has been used to treat rheumatoid arthritis.  With an isoelectric point of 7.47, it is a major component of zinc-binding proteins.   Found in large quantities in hemoglobin, its extraordinary buffering ability in humans arises from the fact that an environmental pH of almost 6.0 is required for it to give up the hydrogen on its imidazole ring.  FTP, name this amino acid whose decarboxylation produces histamine.
An electron donor, it neutralizes singlet oxygen and the hydroxyl radical in the heart.   
histidine