INACTIVATION OF HEN EGG-WHITE LYSOZYME - THE AZIDE RADICAL

Hen-egg-white lysozyme was exponentially inactivated by the azide radi cal. The inactivation yield was pH dependent with a maximum near 5.5. Similar pH effect was found in the protein for the intramolecular one- electron reaction between the indolyl radical and tyrosine. Remarkably , an analogous pH dependence was observed for the catalytic activity o f the hen-egg white lysozyme. This was interpreted as representing the dependence of the catalytic rate on two ionizations of two amino acid s (Asp52 and Glu35). The similarities between the apparent different p henomena lead us to suggest that it is reasonable to argue that at lea st two proton equilibria may perturb the intrinsic pH-rate profiles fo r the tyrOH/trp(.) electron transfer process and radiation inactivatio n. In other words, the pH dependencies that we observe affected by eit her the protein structure or its ionization.