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Arginine modification by phenylglyoxal and (p-hydroxyphenyl)glyoxal: reaction rates and intermediates.

Reaction rates and pathways of two commonly used arginine-modifying reagents, phenylglyoxal (PGO) and (p-hydroxyphenyl)glyoxal (HPGO), were investigated by spectrophotometry. The initial rate at pH 9.0 of PGO with arginyl compounds was found to be 15 to 20 times greater than that of HPGO in the absence of borate but only 1.6 times greater in the presence of borate. Time-resolved spectra of HPGO reactions with arginines revealed, in contrast to the relatively simple spectra of PGO, at least two spectrophotometrically identifiable intermediates, one non-absorbing at 336 nm and the other absorbing at 458 nm. The 458 nm absorbing intermediate species was no longer detectable in the presence of borate.