According to Webster's Third New International Dictionary, the words SISTINE, CYSTINE and CYSTEINE are pronounced in the same way -- a homonymic fact which overtaxes my imagination. The latter two are sulfur-containing amino acids, and ambiguity in spoken English is so real that the preferred dictionary pronunciations are seldom used: CYSTEINE most often becomes a three-syllable word, /sis tay een/, accented on the second syllable so the hearer knows with certainty what the speaker means. In the same fashion, HOMOCYSTEINE and HOMOCYSTINE are in practice pronounced differently, although dictionary preference is for homonymy, rhyming with SISTINE. Note also BENZENE and BENZINE, where a chemist may speak of "benzine-with-an-I" or "benzene-with-an-E".
Wolpow, Edward R.
"The Cystine Chapel,"
Word Ways: Vol. 13
, Article 4.
Available at: https://digitalcommons.butler.edu/wordways/vol13/iss3/4