“As the largest known protein, titin also has the longest IUPAC name of a protein. The full chemical name of the human canonical form of titin, which starts methionyl… and ends …isoleucine, contains 189,819 letters and is sometimes stated to be the longest word in the English language, or of any language. However, lexicographers regard generic names of chemical compounds as verbal formulae rather than English words.”
https://en.wikipedia.org/wiki/Titin#cite_note-60
“As the largest known protein, titin also has the longest IUPAC name of a protein. The full chemical name of the human canonical form of titin, which starts methionyl… and ends …isoleucine, contains 189,819 letters and is sometimes stated to be the longest word in the English language, or of any language. However, lexicographers regard generic names of chemical compounds as verbal formulae rather than English words.”