The Role of Tryptophan and Divalent Sulphur in the Action of Atomic Hydrogen on Lysozyme in Aqueous Solution

Abstract

The effect of atomic hydrogen on lysozyme in aqueous solution has been investigated at different pH, total doses of H atoms and different initial concentrations. As well as inactivation, changes in the ultra violet absorption spectrum, due to tryptophan, formation of sulphydryl groups and H2S, associated with attack on disulphide bonds, have been measured. The decrease in the 280 nm absorption is consistent with attack on the tryptophan residues. Intramolecular transfer of the free radical centre is assumed. The effect of increasing enzyme concentration shows that the intramolecular radical chain terminates when the odd electron becomes paired by encounter with another lysozyme radical. As found for trypsin, the formation of H2S is less when tryptophan as well as tyrosine is present in the enzyme.