Alkylating free thiols

Incubate proteins at RT for 30mins in 10mM DTT.
Incubate proteins at RT for 30mins to 25mM iodoacetamide IN THE DARK. Iodoacetamide dissolves poorly in H20, make 0.5M stock
Dialyse out iodoacetamide, DTT and iodine IN THE DARK.

Note that the iodine produced by the alkylation reaction damages the protein

Iodoacetamide MR: 184.96 g/mol
DTT MR : 154.3 g/mol

Ref: Hirs, Methods Enzymol. (1967) 11: 199-203