Coupling of p-nitropnenyl diazonium, fluoroborate to bovine chymotrypsinogen A and α-chymotrypsin

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Abstract
P-Nitrophenyl diazonium fluoroborate couples at the ε-amino groups of lysyl residues of bovine chymotrypsinogen A and α-chymotrypsin in 0.5 M acetate buffer, pH 5.0. The reaction products are identified by spectral comparison with the model compound bis-(p-nitrophenylazo)-ε-amino-n-caproic acid. The reaction with the zymogen is about four times faster than with the active enzyme and this difference is independent of protein concentration. However, in the presence of 8 M urea, the reaction occurs at the histidyl groups at an equal rate. This suggests that of the groups that could undergo coupling, i.e. histidyl, tyrosyl, and lysyl, only the latter do so in the native proteins; moreover, chymotrypsinogen appears to have more such lysyl residues than does chymotrypsin.

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