Why is DTT used in detecting caspase activity?

DTT is widely used for disruption of protein disulfide bonds. It helps minimizes aggregation related to disulfide bond formation that can occur under oxidation during the breakdown of cells. To avoid such aggreation, add DTT to your homogenizing buffer.

DTT helps protect against some proteolytic attack and will not affect enzyme assays, unless it is a redox-regulated photosynthetic enzyme.