In this capacity, it protects cellular protein thiol groups, which would otherwise become covalently modified; when all GSH has been spent, NAPQI begins to react with the cellular proteins, killing the cells in the process.
Grazas a esta capacidade protexe os grupos tiol das proteínas celulares, que doutro modo serían modificados covalentemente; cando se consome todo o GSH, a NAPQI empeza a reaccionar coas proteínas celulares, orixinando a morte celular.