Dimers formation by cytochrome c-catalyzed oxidation of tyrosine and enkephalins

Cytochrome c in the presence of H2O2 is able to oxidize tyrosine and enkephalins into the corresponding dimers linked by a o,o'-biphenyl link, as evidenced by the spectral and HPLC analysis. Also amino acid analysis of the hydrolysates from cytochrome c-treated enkephalins provides evidence for the presence of dityrosine. Kinetics of the oxidation was followed both spectrophotometrically and fluorometrically. The reaction rate depends on cytochrome c and hydrogen peroxide concentrations. For the first time it is demonstrated that the o,o'-biphenyl link of dityrosine can be formed by the action of an enzymatic system alternative to peroxidase. Some general considerations on the possible consequences of these reactions inside the mitochondrion are outlined.