The effect of radiation-induced reactive oxygen species (ROS) on the structural and functional properties of yeast alcohol dehydrogenase (YADH).

PURPOSE

To determine the mechanism underlying oxidative modifications caused by radiation-induced reactive oxygen species (ROS) and elucidate their effect on the structure and function of yeast alcohol dehydrogenase (YADH), a zinc-containing protein.

MATERIALS AND METHODS

YADH was exposed to water radiolysis products in an air atmosphere. YADH oxidation products were determined by spectrophotometric and spectrofluorimetric methods. The extent to which oxidative modifications affected enzyme activity was also studied.

RESULTS

Water radiolysis products oxidized thiol groups leading to the release of zinc ions and the destruction of tryptophan and tyrosine residues. Those processes were accompanied by alterations in protein structure such as increased surface hydrophobicity, greater tryptophan accessibility to acrylamide, and changes in the secondary structure. Structural modifications were correlated with lower enzyme activity.

CONCLUSION

During the process of functional and structural changes in YADH exposed to reactive oxygen species, a key part is the oxidation of cysteine residues attached to zinc and the release of zinc ions from the molecule. It may be assumed that ROS induce similar changes in many other zinc-containing proteins.