Dityrosine as a product of oxidative stress and fluorescent probe.

Dityrosine can be a natural component of protein structure, a product of environmental stress, or a product of in vitro protein modification. It is both a cross-link and a fluorescent probe that reports structural and functional information on the cross-linked protein molecule. Diverse reactions produce tyrosyl radicals, which in turn may couple to yield dityrosine. Identification and quantitation of dityrosine in protein hydrolysates usually employs reversed phase high pressure liquid chromatography (RP-HPLC) or gas chromatography. RP-HPLC of protein hydrolysates that have been derivatized with dabsyl chloride gives a complete amino acid analysis that includes dityrosine and 3-nitrotyrosine. Calmodulin, which contains a single pair of tyrosyl residues, undergoes both photoactivated and enzyme-catalyzed dityrosine formation. Polarization measurements, employing the intrinsic fluorescence of dityrosine, and catalytic activity determinations show how different patterns of inter- and intramolecular cross-linking affect the interactions of calmodulin with Ca(2+) and enzymes.