Luminescence of ribonuclease A

Abstract

The effect of disulfide bonds on the phosphorescence properties of tyrosyl residues of model compounds and ribonuclease A was investigated. 1. 1.|The tyrosyl residues of polytyrosine, insulin heptapeptide, lysine-tyrosine copolymer, and cysteinyltyrosine are characterized by luminescence ratios ( q P q F ) which are close to 1. The phosphorescence emission decays in an exponential manner with phosphorescence lifetimes (τ P) fluctuating between 2.3 and 2.6 sec. 2. 2.|The cystinyl-bis-tyrosine peptide exhibits an abnormal behavior in its luminescence properties when compared to free tyrosine. Its luminescence ratio ( q P q F ) is equal to 0.2 and its decay time ( τ P = 0.2 sec) is shorter than the value of free tyrosine. 3. 3.|Ribonuclease A is characterized by a luminescence ratio of 0.58 and by a phosphorescence decay time of 1.4 sec. Reductive cleavage of the disulfide bonds brings about an increase in the phosphorescence yield ( q P q F = I ) and phosphorescence decay time ( τ P = 2.3 sec). The low phosphorescence yield of ribonuclease A is related to a quenching effect exerted by the disulfide bonds on the triplet excited state of tyrosyl residues.