  Recent literatures reported blue-green emission from amyloid fibril as
exclusive signature of fibril formation. This unusual visible luminescence is
regularly used to monitor fibril growth. Blue-green emission has also been
observed in crystalline protein and in solution. However, the origin of this
emission is not known exactly. Our spectroscopic study of serum proteins
reveals that the blue-green emission is a property of protein monomer.
Evidences suggest that semiconductor-like band structure of proteins with the
optical band-gap in the visible region is possibly the origin of this
phenomenon. We show here that the band structure of proteins is primarily the
result of electron delocalization through the peptide chain, rather than
through the hydrogen bond network in secondary structure.
