DTT, also known as dithiothreitol, is a reducing agent that can be used to prevent the oxidation of cysteine residues in proteins. It works by reacting with disulfide bonds to convert them to thiol groups, which can then participate in disulfide exchange reactions. The amount of DTT that you should add to prevent cysteine peptide oxidation will depend on several factors, including the concentration and stability of the protein, the presence of other reducing agents or oxidizing agents, and the desired level of protection against oxidation.

DTT is a reducing agent that can be toxic to some organisms, including mice, when ingested or injected. Therefore, it is important to consider the toxicity of DTT when using it in any application, including as a component of a vaccine.

The toxic effects of DTT in mice may vary depending on the dose, route of administration, and the specific strain of mice used. It is generally recommended to use the lowest possible concentration of DTT that is effective for the intended purpose, and to carefully monitor the health and behavior of the mice for any adverse effects.

In general, DTT is typically added to protein solutions at concentrations of 0.1-1 mM. However, for subcutaneous injection into mice, it may be necessary to use a lower concentration of DTT to avoid toxicity. It is recommended to carefully evaluate the toxic effects of DTT at different concentrations in mice and to determine the lowest concentration that is effective for the intended purpose.

It is also worth noting that DTT is not the only option for preventing cysteine peptide oxidation. Other reducing agents, such as tris(2-carboxyethyl)phosphine (TCEP) or β-mercaptoethanol (BME), may also be used. These agents may have different toxicities in mice and should be carefully evaluated before use.