I already used the 5 reducing agents supplied with the enzyme, can I use another reducing agent besides cysteine?

The ready-to-use reaction buffer additive has been optimized to provide full enzymatic activity without affecting the disulphide bridges between the light chain and Fd region of the heavy chain, keeping the Fab intact. We recommend preparing a fresh solution of pH neutral cysteine, for use the same day, with a final reaction concentration of 2mM.