- an essential amino acid, C3H3N2CH2CH(NH2)COOH, that is a constituent of proteins and is important as the iron-binding site in hemoglobin. Abbreviation: His; Symbol: H
- a nonessential amino acid that occurs in most proteins: a precursor of histamine
complex amino acid, 1896, from German histidin; see + chemical suffix -idine.
- An amino acid that is essential for tissue growth and repair.
- An amino acid that is essential for children but not for adults. Chemical formula: C6H9N3O2.