ELECTROCHEMICAL MODIFICATION OF LYSOZYME - ANODIC REACTION OF TYROSINE RESIDUES

Preparative electrooxidation of lysozyme at copper electrodes held at potentials around 1.2 V vs. a saturated calomel reference electrode in duces the formation of a yellow chromophore with a concomitant decreas e in the pI of the protein. Ion-exchange high-performance liquid chrom atography revealed two new lysozyme species with pI values of 10.8 and 10.7 (lysozyme-11.0) which bear the chromophore. Sequence analysis of these two species showed that protein with lower pI was modified at b oth Tyr 23 and Tyr 20 and the other exclusively at Tyr 23. Ribonucleas e A, subtilisin BPN' and BSA were also found to produce the same chrom ophore using similar electrochemical reaction schemes. Characterizatio n of the chromophore by a variety of techniques revealed that it is ap parently 3-nitrotyrosine.