I am not sure what exactly your problem is; you need to give more details in your question.
What metal are you talking about? Is it a salt of a metal or the unaltered metal itself? What is your setup? Do you perhaps in your setup create a electrochemical cell, a connection to another metal, which is reduced via your metal?
But at pH-values of > 11, cysteines and methionines will likely themselves be oxidized.