 The thiolate is oxidized to a sulfenic acid, which is converted to a sulfenyl amide after reacting with the adjacent Ser216 residue.This modification of the Cys215 residue prevents further oxidation of the residue which would be irreversible, and also induces a structural change in the cleft of the active site such that substrates may not bind.This oxidation can be reversed through reduction by glutathione and acts as a means of regulating PTP1B activity.