Infrared absorption of tyrosine side chains in proteins

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.