Abstract
Poly‐L‐tyrosine absorbs strongly at 1515 cm.−1, and a band at this frequency has been found in a number of proteins and has been assigned to the tyrosine residue. The assignment was confirmed by examination of spectra of deuterated proteins, which usually exhibit a residual band at 1513 cm.−1. In proteins, this band correlates linearly with known tyrosine content, but the point corresponding to poly‐L‐tyrosine itself does not fall on the correlation line. The possibility and limitations of using the infrared method for tyrosine determinations is discussed.