Hi Ryan,

Toxicity depends on the system you are working with and whether in vivo or in vitro. Suitable reducing reagents depend on what is being reduced. Glutathione has a redox potential of -240 mV and is present in nearly all living organisms. By altering the ratio of reduced (GSH) to oxidized (GSSG), you can achieve a range of redox potentials. A number of proteins can also be used to achieve reduction. E.coli can be grown in the presence of up to 10mM dithiothreitol. Perhaps the attached reference will help.

Article Redox Potentials of Glutaredoxins and Other Thiol-Disulfide ...

Cysteine can be used as a relatively safe (ecofriendly) mild disulfide reducing agent, followed by Dithiothreitol and mercaptoethanol (under in vitro conditions).

Thank you all for your answers it is most helpful.

You could add Tri Hydroxypropyl phosphine THPP available from Sigma Aldrich sometimes it wirks better than TCEP

Redox couples such as GSH/GSSG and Cysteine/Cystine are friendly to most proteins followed by reducing agents mentioned above

Bhagwan apka bhala kare